It's the give and take that won her over. Knowing that she could choose to be in charge or to submit to him, and he would return in kind... She likes that aspect of their relationship. It sates the part of her that craves power. Plus, it's the key for him to unlock her heart - not that either of them truly need those kinds of feelings, of course.

She lets out a slight moan as she feels his hardness against her. "Yes...shall we?"