Actually the aliens didn't do that to her, in the game/anime she was a Valkerie warrior, and then in a battle she was captured, and turned into a sex slave (as all female warriors do, lol) and then the people who own her they change her body to fit their clients wants such as a penis, amputation, the freaky nipples, a bigger vagina so that this one monster which can hold her in the palm of his hand can do the dirty with her.