I wish I didn’t have a job like this… I’d rather talk to retards all fucking day long than deal with dipshits that think they know what they are doing on computer and won’t listen to what you are fucking saying to them.
Thank god I don’t phone consult anymore
I never use a machine I care about. I have a pretty bare bones laptop that I generally use along with a USB to SATA/IDE adapter. I just do a scan after words to be sure I am OK. I reformat it fairly often just for shits and giggles.
If it was me I’d take the drive out and put it in another desktop with up to date virus defs. Have it do a full scan on the drive, then once it’s been cleaned copy off what ever data she needs to save (pictures, documents, MP3’s etc).
Then do a quick format, toss it back into her computer and reinstall windows.
But that’s just me, a software engineer who’s been dealing with computers 8 hours a day, 5 days a week for the past 10+ years. 
knoppix. It’s linux that you can boot with full graphical interface from a CD. Boot it, save your files to a USB stick, reformat, install antivirus software, copy files back to computer, call in the favor she owes you.
Mandriva offers a distro that boots nicely off a CD too IIRC.