Looks like an optical illusion created by her shirt to me.
@AC3BOY: her nipples are really high because she got a crappy boob job. In a lot of her sets where she’s topless and covering them with her hands/elbows/tape/whatever, you can tell that they are unnaturally high. See the Action Girls “black tape on the nipples set” for example.
EDIT: Crap, somebody types faster than me, apparently!