SuperAdministrator worked but...
My friend was able to get the super admin account to work which allowed her to run CHKDSK /F but it errored out with that same "unknown error". I talked her through trying a System Recovery but that also crapped out saying that none of the recovery files was valid.
At this point I've asked her to leave her computer with me for a few days to see if I can get it working. I plan to run a virus scan from a CD and then try see if I can run a backup before trying to repair the OS from the OEM disk. If that doesn't work I suspect I'll have to reformat her drive and restore her data as best I can.
Anyone have any other suggestions?