Sounds like a re-re-install is in order. I will assume she has a valid COA for Windows XP home. In that case, locate any valid Window XP Home installation disk (she will not be able to active the XP Pro - it will be dead in 30 days) and do a CLEAN
install of XP using that disk. You can change the COA number to her valid number (hopefully that number is shown somewhere on the machine) using the procedure here
. A followup activation will most likely be required.
As for the reinfection. MTTI (mean time to infection) using an unpatcher copy if Windows with no firewall is 20 minutes. I've seen system infected from the net in less than 30 seconds. You MUST be sure a firewall is active before getting anywhere near the net after a clean install of Windows. Then head directly to the Windows Update site and install All critical updates.