I say RENT. RENT has been an inspiration to me and I bet it has been to most people on this site. RENT is the perfect musical and the OBC would be an awsome gift.
If your friend is extremely new to the genre, maybe you should start off with Chicago. They can be brought in by the accessible movie, and then when you give her a CD, give her Chita or Bebe, and I think it wil be welcoming in terms of associating the style of music with visuals, even though the movie is, of course, very differnt than what you would see onstage.
A man is getting along on the road to wisdom when he begins to realize that his opinion is just an opinion.
I agree with everyone else, Rent or Wicked would be best. Should you decide on Rent, however, I'd try to get the double disk because the highlights don't cut it *but this is coming from a major RentHead*. Wicked is a great choice as well. =P