I'm not sure this is possible from the XP GUI, but I know you can do it from DOS:
C:\> subst D: C:\her\stuff
You need to re-assign this one for every boot, so you can add it to the startup folder or something.
Suggestion #2 (and probably the easiest one): Enable windows file sharing, share her directory (or "folder" as it's called in the Windows world), map it as a drive (D:) on the same computer. This drive will remap itself on every login.
[Edit: I think I misunderstood the question]
