Ok. So do you have a question about the situation that we can help you with? Did you just want our advice in general?
You could check the laws in your state. Statutory rape (when an older person does sexual things with a much younger person who is 18 ) vary a bit from state to state, although I believe that what she did might be a felony in every state.
If you want to get into dominance and submission, that's all right, but be safe about. Subs usually do have limits and safe words.