Well, I do live under a rock, and I don't know anything about her beyond what we saw in the movie. Having her there was a crass marketing move, her songs and general existence had nothing to do with the movie's plot, although at least they kept her involvement to a minimum. I'm not into pop, and I didn't care for her music in the movie.
Of course, the movie wasn't all that great to begin with.
Cute pony design, though.