Create a boot floppy (or CD, but if she has a floppy then this is less "technical") with the memtest floppy image:
Memtest86+ - Advanced Memory Diagnostic Tool
Boot from said floppy, let it run for a few passes. Errors present mean problems with memory, errors not present mean look elsewhere.
Also, have her or someome else check the capacitors on the motherboard around the socket. Any swelling on the tops means capacitor failure, and therefore board failure. This commonly causes OS errors, but not reboots. Reboots usually mean PSU failure, but not 100% of the time. The caps can be replaced (I can do them easily enough) but most techs are not that skilled, and most electrical engineers or electricians are not that cheap.
If it's just a BSOD reboot, then disregard the PSU mention for now. Think caps, memory, or hard drive corruption.