Windws Explorer Display Changed

A friend of mine came to me tonight with a problem and I don't have the answer for her. Windows Explorer used to display the files and folders of a disc or folder on the whole screen. Now she gets the display on only the right part of her screen; the left side lists all the discs and other folders (library, favorites)on the left side. For her this is very annoying and distracting. It also changed the position of the icons displayed which she finds really annoying. She gave me two screenshots so I'll attach them here. The top one shows how she used to have the display and the bottom one shows the way the display is now. If someone can help her I'll pass along the answer to her.

The difference on the left is the navigation panel, that can be easily shown and hidden.

Click on Organize => Design => Navigation panel to toggle it and it'll change between both of your screenshots.

Thank you Alejandro85. My friend is ecstatic that you solved her problem. It's slightly different on her Windows -"layout" instead of "design" - but it worked the same way. My friend sends you her very big gratitude.

Thank you RolandJS though I don't know what the "invisible bar" is (because it's invisible? )

Thanks for the explanation. I'll see if I can find it, too.