Hey everyone! I just HAD to thank you for the help here. I ran SFC and it fixed everything.

I'm still a little concerned, as when I ran it, it complained that it was not the correct disc. Well, at first I accidentally hit "Retry," and it proceeded to progress a significant portion. Then it complained again, and I clicked "Retry" again. I had figured that at this point I had little to lose (all the data was backed up). So I just kept hitting "Retry" until the progress bar finished. After a brief restart, all I had to do was reload the NIC drivers (already on the system), and reselect the correct audio device in her sound settings, and the computer was fully functional again.

I suspect the disc we were using was just not the exact disc for that install of Windows. It was the only one she had, though, and it matched the Windows version.

Whatever, it totally worked, and I thank you guys for the help. And thanks to you, Trevor.