I think he is on the right track. I also think that that could be an authentication issue.
when you say at random, if that means that she doenst use it for extended times, it may be that the server disconnects her after a timeout. also, another peer maybe accessing the same mapped drive and disconnecting her (which shouldnt be happening)
Are you using logon scripts? If not, you may want to look into it. Much easier than manually mapping evertime there is a server reboot.
but i think its to do with the 2k server because at our school, everyday (after server was shut off and turned back on the next day) all our mapped drives needed to be remapped even though it was at the same path. but once they were mapped they wouldnt disconnect after you mapped them.