ohhhh haha. Got it. It's honestly not even that with her; I get crushes on some actresses simply for the roles they choose and persona they put on. She happens to be someone I think is badass in terms of the characters she plays, even though I realize there's no reason to assume this reflects on her personality in real life. It's just a coolness I've constructed around her, and it makes her attractive to me. The breasts are just a plus.
It's the same reason I have a thing for Tatiana Maslany, which I remember some posters here not understanding, haha.