What's the BIOS version? Have you tried the A09 (last) version dated 10/5/2001? Maybe it'll straighten out whatever the problem is. Check [link|http://support.dell.com/us/en/filelib/results.asp?sid=DIM_PNT_P4_8100&lang=EN&lib=1&os=WNT5&searchtype=filter&devid=308|here] on Dell's site.
A post is archived in Google's USENET archive say that Dell machines often act better on using a generic version of Win2K - e.g. [link|http://www.experts-exchange.com/Databases/MS_Access/Q_20097662.html|WarrenGlass's comment] - so going to Dell's version may not be an answer.
If you're running the latest BIOS, then maybe small claims court is an option.
Dimension 8100s on ebay are going for < $500-$600 or so with no OS.
If she just needs a Win2K machine there must be a cheaper and less aggravating way to get there. Perhaps buying a < $250 barebone mini-chassis boxes from NewEgg (if her expansion cards will fit), or this [link|http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2078637553|Compaq Presario with WinXP] for $299 ("buy it now") or less on ebay. (I've had good luck with Compaq Presarios running Win98 and WinMe but I know they have bad reputations.) There may be some other machines on ebay that already have Win2K and reasonable prices, but none came up in my quick checking.
Having a friend with computer problems who isn't able to spend any money to solve them really bites. :-(
I hope you get it figured out. That's about all I can suggest. Good luck!
Cheers,
Scott.