The D90 is a great camera and does 720p video however it is discontinued and its replacement, the D7000 may be overkill for a beginner (as would be the D90).
If she is new to real photography then you could maybe start with a Nikon D3100 - $650 ish. It takes great photos and HD video. It comes with a 18-55mm lens which will give you some wide angle but no zoom. You have a couple of options for bringing things closer - either a 70-200mm for about $300 or, to avoid changing lenses, the Nikkor 18-200mm VR for about $700.
If you don't care about video, get a used D40. A great camera. You should be able to pick up a used one for under $400 with lens. I started with a D40 and moved up to a D300S.
I would suggest you go to your closest Ritz and get a feeling for the size and weight. The 40/3100/5000 are quite small and light. The 90/7000/300S are monsters.
http://www.flickr.com/photos/tomroyal/2168822100/#
Lastly, if you are looking at a Canon or Nikon, don't worry about specs, especially megapixels.