yes you can. as long as she is part of your developer team (which, if she is testing an app that you developer - she is) then you will be fine with adding her.
I'm sure lots of developers who have friends and family with iphones are doing that to test out their apps before sending it out to the general public.. HOWEVER be aware that she might get a tad pissed, as 3.0 is not stable and not everythign is working on it yet