I'm not sure why you'd need a specific "reason" for a predator to be female. It could just totally be a non-issue, she happens to be female, end of story. Female beings exist, there's no "reason" for it. And though big bouncing boobs would bother me, I'd be okay with small breasts (it depends on whether you take the books as canon or not, but there are hints to indicate female predators do in fact have breasts.)