Are you sure your friend is that enthused about ballet? Ballet is one thing to see in person, and an entirely different thing to watch on a TV. My suggestion would be to buy her tickets to some local production instead. However, if you don't want to shell out the money a Cirque du Soliel show would be more entertaining on a TV, or something with dance and dialogue like Swing Kids, Tap, Shall We Dance, Strictly Ballroom, etc., etc...
I danced for quite some time as well and watching a Ballet on a TV screen would be kinda lackluster, imo.
edit: If you're going to buy her a movie about ballet, then buy her...Billy Elliot, it's very good, even for people who don't care much about dance.