This sounds very similar to how it went down with my wife and I. Happy to chat about our experience with her ex and how we slowly initiated role playing him fucking her and went to her DMing him and then him telling her he was coming to town for work and me encouraging her to spend the weekend with him. The whole way I felt in control of the situation, but reflecting on it later I realize she guided the entire situation for me to approve of. Her acting like she wasn't sure was just her way of feeling out my feelings, She wanted his big cock the whole time, she just pretended like she didn't need it so it would be my idea... my advice is to take it slow and let her guide it at her pace... as long as you know you want this to happen and have truly thought about how you will feel afterwards. I thought i wanted it and I had fantasized about it for years before hand, but when it actually happened I went through a lot of emotional turmoil. It is a big step from fantasy to reality and while I am happy she did it, I am still conflicted and we haven't done it in a while and may not again. it is a huge step no matter what anyone says. Happy to answer any questions.