There are a few issues with fitting a Judy DH, the Judy came out when 1 1/8th headsets were all but standard, apart from the very last Bontrager Privateers (1997-1999 models), all of them were 1" headtubes, if the Judy isn't 1", which is very likely it isn't going to fit. Judy's are long outdated by today's standards, the Marzocchi is old, but will ride better than a Judy of the same age.
The headtube issue will also affect choosing any modern fork, as most are only produced in 1 1/8th" or tapered now, 1" is very rare, this could even cause issues in getting a rigid fork. (all this is on the basis that the bike is a mid-90's model, which will be either a Santa Cruz build or Wisconsin Privateer from 1996/97)
Why can't you get the Z2 serviced? they aren't that hard to service, see here for manuals
http://www.enduroforkseals.com/id12.html,
If your friend does choose to get a replacement fork, the old one should have some value if selling on ebay, as Marzocchi's of this age are repairable, and have a retro following.
Not sure why a rigid fork would limit her off road riding, we all managed without them BITD.