"Above all, be the heroine of your life, not the victim." Nora Ephron
What is her definition of happy, how has she gotten there and what steps has she taken for this happiness to have found it's way to her?
Kind of a bitter pill to swallow IMO.
Not going to keep sacrificing what I want in life, for her sake. Not post A. Not anymore
Your arguments for one.. well in a stable relationship and both of you wanting another child, perfectly lovely.
I would be asking your WS why she is happy. Might be something to bring up with the MC.
The major difference, and I suspect the critical difference, between the way my H stated his feelings versus the way your WS stated hers, seems to be that my H would say, "I'm really happy. I'm happy to be here with you, and I'm so sorry that I hurt you so badly and jeopardized all this." Could it be that your WS's message was poorly sent, but was meant to be an affirmation of what you bring to her life? Would it help you to further discuss why she said what she did--and why she chose that time to say it? Was she being self-centered, or could she have been trying to make you feel secure in the relationship by telling you that she was happy with you?
These are just my thoughts coming from my own experience; perhaps they pertain to your situation or not. Either way, I hope you get what you need; I'm rooting for you, Nogoingback.
BTW, if your daughter does end up being an only, that's ok. There are lots of good things that go with being an only. I have just one, and he is my treasure! And he has never asked for or wanted a sibiling -- I think he likes not having to share!