My WH got a new secret email account with his AP the day he promised me he would break it off with her. He knew exactly what he was doing.
We cannot rationalize their actions while they were in the A. Believe me, I have done what you're doing a million times, and each time I just have to tell myself he was in his "fog" of the A. If I didn't do that, I would drive myself insane.
I think in your case, she said that while thinking about you, but she wasn't thinking about you. She was probably looking more for his response to that remark...something like, "It won't be this way forever." Who knows what she was looking for.
The bottom line: You have to look at her actions from NC on. If you feel that she really wants your M and is doing everything she can to make you feel safe and secure in your M, then take that for what it is worth.
Write down all of these thoughts in a journal to bring up at MC with her (and post them on here, of course, so we can help a little bit in the meantime). It helps to have a third party present to help the communication along for these kinds of questions.
Honestly, you cannot try to figure out the things that were said or the "why" of what happened, because our WS's are in such a fog during the A that they probably don't know themselves.
I hope this makes sense. I'm sorry you're hurting. I'm sorry for all of us hurting!!