Julian....boy !! You are gonna have so much fun with the D300. I like natural light, say from a window but not direct sunlight into the subjects face. I like to try and get a catchlight in the eye. I'd suggest longish focal length, wide open. Adjust ISO to get a low as possible shutter, maybe as low as1/60th.
These situations make good use of a reflector. Use the time till you get your hands on the D300 to observe her and see if you get the lighting and pose sorted so you'll have a good idea where to start.
Have fun mate, you're gonna love it.