Thank you for the replies. Not one of you said anything that I haven't already thought about.
She (A) and I finally got out alone a couple of nights ago, just the two of us. We both had some things that needed to be talked about. It was nice, but I didn't walk away feeling that she had a complete understanding. Ok, for one, she keeps talking about leaving her BF, but knows she's not ready to do that now. I told her that was fine, but in order for this to work for any of us we all had to be completely open and honest on all parts, including her BF. She tried saying that she wasn't lying, she just wasn't telling him everything (Umm, is this an age thing, because I am totaly rolling my eyes at that statement). I couldn't have been anymore adament on the honesty. I also told her that I wasn't looking for a swap or for her and her BF to be with us... just her. She said she knew that and understood that, then continued to tell me that her and her BF want to have a threesome with my BF. Ok, this was an issue because I made it clear that was not something we were looking for. I was annoyed. She also keeps bringing things up that were discussed between my BF and her, things I thought we staying between him and I. This is an issue I have already, after the fact hashed out with my BF. I told my BF from the begining that this better not be about the two of them wanting to be together, and she is just "willing" to be with me. She assured me this wasn't the case and that she really likes me. She even said she doesn't normally like girls so quickly, that I was different. I believe her that she likes me. I told her we invited her into our home prematurally, and of course she agreed.
I really want this to work, and I am going to continue to feel out the situation. I told her I wanted to take things slower than we were. She agreed. I just hope that she really understands how important the honesty is, and how sex is not nearly as important as that. She's never been the third, said she was always part of the primary couple with a partner. So, taking it slow works for her. But, I guess we will see. Since it is all new, I am willing to work on getting the kinks out and seeing where everyone really stands. I will be paying better attention to the honesty and calling her out on things I am not ok with... it really is the only way for this to work.