If it restarts after trying to enter safe mode, I'd test the hard drive. It does a big read/load of a bunch of drivers when you select that, and a restart indicates some kind of hardware/windows error.
I'd try the standard seatools and memtest. Then try a live CD/USB. Then try to repair windows.
try booting into safe mode and running a chkdsk /x /f /r
sfc /scannow
also, download and burn a windows xp recovery iso to a dvd and boot to it.
run the repair
If you can't seem to get windows to run after recovery, do a load factory defaults on the bios and try reseating the cmos battery.
Then get a pata usb drive adapter and mount it onto another system-unit and extract all the data she needs.
Her PATA drive is probably pretty old and old drives are known for being unreliable and slow, especially ones that use parallel communication.
sfc doesn't work on XP, it needs the original CD.
Honestly, the computer is probably near death if it came with XP. It must be over 10 years old by now, and probably never had the dust cleaned out. I imagine you are looking at a dead HDD.
I'd just see if you get the files off and replace it. It's cheaper to buy a new system (~$200) than the cost of labour per hour to get that thing working, or even replace 1 part.