Out of those two, I would be inclined to say Dragon Age. It's more self explanatory both mechanically and story wise. My other advice would be, whatever you choose, if possible play it with her. As a first time gamer, she may be more inclined to come back to it if you can make it an enjoyable experience that you share.
NWN 2, as has been mentioned, is heavy. Whilst I would say it is the better RPG, it's not the best starting point. It's like I say about comic books. You would not start out someone who had never read a comic with the works of Alan Moore. You'd give them something lighter to get into the medium with, like The Dark Knight Returns.
What he said. It's just an easier game to digest, to the disappointment of RPG fans, but perfect for a first timer. My friend's wife plays it on PS3 so it must be good.
On the lol side, I wonder if she'll pick Zevran or Alistair...or Leliana :P