Yeah well that's the tricky bit, innit. How many drives have you got?
ETA: Actually I'm not sure how you'd do it. Gonna have to ask around a bit. If you have an extra drive or two you could install to one of those and then try hauling out the contents of C, but there's probably a better way of doing it.
She can install on a partition. Or if she has more then one drive she can install on another drive, or she can even make a USB housing and make an external USB hard-drive... But that might be a little too complex for her. In any case, depending on her BIOS and Hard rive, she might not be able to partition until she reformats, but if this is a pre-bundled install, then it is more then likely her drive will already be partitioned so the only thing she needs to do is installed on the "recovery" partition, and boot from that partition which will when logged in give her access to her "C drive" - the failed paration, she only either extract the stuff she needs or, she could try to repair it, by copying her windows folder (from her working OP) and pasting it to her corrupted one and replacing all files and then try booting from the original.
@ Berbs lol, @ your brother, but if I did live near you I could fix it for you, you know being an overclocker and someone who builds his own computers. Yeah as long as I could keep my consantration on fixing then computer then you in your high heels and risque dress.