Bizarre Connection Problem Affecting Only One System on Network

My girlfriend and I have been getting strange behavior out of her laptop and wireless connections.

Misc details on hardware (for reference):
Router: D-Link DIR-655 wireless router
Modem: Motorola SURFboard modem.
Girlfriend's Laptop's Wireless card: intel wifi link 5300 agn
My Desktop Wirelss card: 802.11n Wireless LAN card
Our operating systems: Windows 7 for both computers.
Router Security: WPA/WPA2 Personal
Connection speed: 65.0 mbps currently, on my (functioning) desktop.
My girlfriend's laptop and my desktop are sitting right next to each other, with only one thin wall separating us from the router. The router is literally pushed up against the very same wall that our desks sit against.

We started to use this wireless router and modem fresh and new in October of last year. Up until about this February, both her laptop and my desktop computer have been able to connect to the internet just fine, with very fast speeds and low ping. The highest our ping would ever rise to would be about 60 ms on a "bad" day. Well, in February, my girlfriend's laptop started to experience intermittent, extremely high lag spikes and slow connection speeds completely out of nowhere, while my desktop is completely unaffected. We could both go to the same webpages, play the same games, and generally go about life as usual but for some reason and entirely out of the blue, my girlfriends wireless had begun to slow down entirely. We play a lot of games together: we'd be playing the same game, with each other, at the same time, and while in the past we would both run at 40-50ms ping, all of a sudden I will be at 40-50ms and she will be at 80 then 600 then 300 then 1500 then 700, etc. Her webpages load slowly, and youtube is barely functional on her computer. While the problem is still intermittent (slow and laggy for hours on end, then fine for a couple hours, then slow again) it has only increased in frequency of occurence over time
. It's very frustrating. And, again, while all of this is happening to HER laptop, MY computer is running absolutely fine. I have had no connectivity problems myself, period. We are both connected to the same network. (Note: we both run the same antivirus programs as well: malwarebytes, spybot search and destroy, and avast!, with all of the same shields enabled and windows firewall. Never used to be an issue)

On top of this, bizarrely, when she uses the small switch on the front of her laptop to switch off her wireless card, I lose connection on my desktop entirely and completely until she switches her card back on.

Things we have tried to solve this:
-Turning router off/on in 30 seconds.
-Turning modem off/on.
-Restarting her laptop.
-Turning off/on her laptop's wireless card.
-Disabling/enabling her wireless adapter.
-Disabling/enabling her adapter drivers, and updating them (claims drivers are up to date).
-Doing a complete reset of the router (back to factory condition, then re-enabling WPA and changing its network name back to what it was)
-Disabling firewalls and antivirus programs.
-Ip release/renew in the command prompt.
-Updating router firmware (the firmware was in factory condition from October*no laptop problems* until about March*laptop problems had begun, then in march we updated the firmware to the newest version as an attempted fix. It didn't help, but the router is currently using the up-to-date firmware, as compared to the firmware that worked in October.)
-Deleting all temp files, and clearing EVERYTHING under "clear recent history" in the Tools menu of Firefox.
-Scanning for malware with all three said antivirus programs.
-The connection is awful no matter whether only firefox with no background programs is running and a single tab up, or if there are several things running at once. So closing down all programs but one, the connection is still slow.

Things of Note:
-Her computer runs as fine and fast as always, at least when it comes to local processes. Her non-internet games and programs load and run just fine, at pretty respectable speeds: only the internet connections are having this problem.
-Her laptop has had heating problems (as always with a laptop)
-We do not give our router any "downtime", even when we are sleeping: we leave it on 24/7 unless we need to reset it.
-Our ISP is Comcast.
-The problem does not seem to coincide with peak times for internet use: it just happens 24/7.
-We haven't tried defragging her hard drive: not sure what that does or if it would help, (I am newb).
-The MAC address of the router is cloned from my laptop, which is almost never on or in use any more (with me using my desktop*running fine* and her using her laptop*busted connection*). Could this be part of the problem?
-As far as I can tell, there is nothing in the router administration page to indicate that it has any settings or preferences in relation to her computer that it doesn't have in relation to mine. IE, my desktop and her laptop all show up on the same lists and have the same settings on all pages of the router administration page. As far as I can tell.
-Her connection does not have the yellow "!" triangle of "limited or no connectivity" on her connection icon.
-It's really really weird that her connection has just up and fried all of a sudden when mine is running just fine, with the same exact OS and firewall/antivirus settings, sitting in the same room, with the same router and wireless network as we have always used.

I have the same D-link router.

It's sometimes required to push and hold the reset button for thirty seconds to clear the router when something goes wrong. After that you can use a configuration file from the routers page at tools/system to replace the settings or redefine the wireless settings manually.

You should be using WPA2 with AES encryption for wireless N.

You will get much faster wireless speeds by using the Wireless N Only setting, 300Mbps is what I get.

You should also try using a different wireless channel, software like Wi-Fi Inspector | Xirrus can help you find a clear channel in your area.

You may want to check your Wireless profiles to make sure it's set up to use the same settings as are defined in the router.

I'm not sure how shutting off the wireless on one machine could knock another machine off line but you might want to check that the Microsoft WIFI miniport adapter is disabled on both machines. You can see it there in device manager.

Picture is from my D-Link DIR-655 wireless settings page.

It would also be helpful if you can post a screen shot of your ipconfig/all from both machines during connection and when it cuts out as well. Sample below.

chev65 said:

It's sometimes required to push and hold the reset button for thirty seconds to clear the router when something goes wrong. After that you can use a configuration file from the routers page at tools/system to replace the settings or redefine the wireless settings manually.

I have tried this in the past, but I will try it again soon if some of these other suggestions don't work! :)

chev65 said:

You will get much faster wireless speeds by using the Wireless N Only setting, 300Mbps is what I get.

Where is the Wireless N Only setting located in the router administration pages? Can't seem to find it yet...

chev65 said:

You should also try using a different wireless channel, software like Wi-Fi Inspector | Xirrus can help you find a clear channel in your area.

Trying this now! But wouldn't this router setting affect all computers on the network, instead of just one?
EDIT: Channel changed to one no one is using (8), slight performance increase but nothing significant yet.

chev65 said:

You may want to check your Wireless profiles to make sure it's set up to use the same settings as are defined in the router.

Checking...
EDIT: Yes, the network profile for our connection is set to use AES and WPA2 (only, as far as I can tell)

chev65 said:

I'm not sure how shutting off the wireless on one machine could knock another machine off line but you might want to check that the Microsoft WIFI miniport adapter is disabled on both machines. You can see it there in device manager.

I was unable to find any device with this name in Control Panel->System->Device manager, on either computer which branch is it located under usually?

chev65 said:

It would also be helpful if you can post a screen shot of your ipconfig/all from both machines during connection and when it cuts out as well. Sample below.

On it!

You can see the wireless N only setting in the routers set up page picture I posted near the top of the page.

It will be the same place for you, from the routers page at 192.168.0.1 click the "setup" tab, then wireless settings left side, then choose "Manual wireless setup" at the bottom of the page. If you are having problems post a screen shot of the page.

The channel problem may only effect one machine, it depends on the driver and other factors, it's just something that needs to be checked out. We need to cover the basics first. :)

For the WIFI mini port adaptor go to Device Manager>network adaptors>expand, it will be there if it's installed.

chev65 said:

For the WIFI mini port adaptor go to Device Manager>network adaptors>expand, it will be there if it's installed.

Oh! I see, I was expecting literally "Wireless N Only", haha. I'm very much a beginner to all this. Enabled the wireless N only option :)

Meanwhile: as edited above (Just posting in here because edits are kind of a dumb way to update information lol) I changed the channel and experienced a moderate increase in performance.

Lastly, there does not appear to be a "Microsoft wifi mini port adapter" under that branch, although there are several WAN miniport adapters and a couple Microsoft ISATAP adapters (whatever any of those are). Included is a screenshot of my own device manager page with hidden devices shown, her list is virtually identical except for the very first device (as hers corresponds to her own wireless card, of course.)

Five seconds till I can get that ipconfig up.

Yes I should have said "802.11n only", much better wireless speeds there.

Device Manager looks ok, the ipconfig/all screen shots from both machines will tell me more.

Gonna be a bit longer: we're grabbing dinner quick and having another scan run as the computer was acting a bit more finicky than usual (I should mention: we have the free version of Malwarebytes *not registered yet*, and it's in that weird state of limbo where it says your trial has run out but it continues to help out anyway.) It says it's found two infected objects so far, so we'll see. Either way, I'm sorry to interrupt and very grateful for all the help so far (her internet is running faster now ((except for some game applications and youtube)) and so is mine, slightly) but I'll post back later with those screenshots.