[knottyb0y]

If you are going to be fear kiting most any melee would work well with a necro. It will be rough for the first series of levels, but once the necro get's they pact heals and if they play smart they can keep you alive long enough to kill a lot of creatures. I wouldn't rely too hard of duoing hard dungeons, but easier blue conning stuff shouldn't be a problem. Fearkiting outside should be a piece of cake if you can get used to following feared mobs.

With that said I think a monk or a shadowknight would both be good duo with a necro. Monks have the high dps, mend and feign death to stay alive when things go bad. SK's eventually will be able t Feign death as well. You'll find as an SK most of your spells will be overwritten by the necro (except for lifetap and probably disease cloud), but the SK should have no problem holding aggro over the necro if it came to that. Another advantage that the SK would have is self invis. With invis the necro and Sk will be able to travel into dungeons or through dangerous areas with little problem.

Monk
High DPS
Feign Death
Mend (combined with necro heals can kick downtime's ass)

SK
High HP
Feign Death (level 30?)
invis and other spells but many offensive spells will be overwritten by necro

A smart necro can pretty much duo effectively with any class, so hopefully your girlfriend reads up on necros and learns the class well. They aren't outrightly overpowered(not to say they are under powered in any way) but played well there isn't much a necro can't kill.