Just wanted to say that I completely agree with this post of Greyskull's:
"I don't think it will hurt her at all to see that this makes you upset, or that it is causing you and her father to argue, this is the reality of the choice she has made. You will support her and once the baby is here you will all make the best of it, however, she doesn't need a sugar coated version of reality, this is going to be fucking hard for all of you, you don't have to be nicey nicey about it."
She needs to know that you are angry, justifiably so, and that anger doesn't always equal rejection.
I also totally agree with everyone who is saying that you need to take some time away just for you, to get support for you, just to be on your own/with the boys and let your H and DSD start to work things out for themselves. If he's so keen to make up for her mother's abandonment, he needs to stop abdicating his responsibilities to you, because she will see it and understand it for the abandonment it is.
Finally, I can't help thinking of that old saying, 'children need love the most when they deserve it the least'. It's clear that you are providing that love to a scared and vulnerable child at great cost to yourself, and you should feel very proud of that. But do make sure you give yourself a break, you can't do this all yourself.