If she has had her ass fucked properly..she wouldn't hesitate to let you fuck it, In fact , would encourage it. My guess is that she enjoys anal play but had a bad experience with an unskilled cock in her ass. If you get her worked up and peeped good..once she feels it slide in..she is all yours. And she will have the best full body orgasm ever..and beg to have her ass fucked a lot more.
