I have no experience of this whatsoever but wanted to offer you my sympathy over what must be a very difficult situation for all concerned. I actually agree with NKF's post.
I don't agree with the fact your husband chose not to have anything to do with his daughter for so long, but the fact is, he did decide to do that, and those are the circumstances in which your marriage has evolved. Now he has completely moved the goalposts - whether or not this is right from a moral point of view isn't really the issue so far as you (in particular) are concerned - the thing is, after a huge long time of behaving one way, DH is now behaving completely differently.
Quite possibly his intensity is motivated by guilt. Maybe he could shut this girl away quite easily while she wasn't "real" but after she made contact he could no longer deny her ? Whatever the motivation for his change of heart however, I think it is up to HIM (and not really the daughter) to reassure you and to try to involve you. This doesn't necessarily mean cosy family lunches etc straight off, but he should - if that's what you want - be telling you what they've discussed, and asking you about long trips, not telling you. It's not fair that he asked you to call his daughter to discuss your worries, because really, the impact of all this on your relationship with him is HIS responsibility, not hers.
I do feel that possibly the OP has had a little bit of a hard ride from some of the replies. She is now paying the price for a decision her husband took - arguably a selfish and irresponsible one - many many years ago, and I think it's unrealistic to expect her to just shrug her shoulders about it, because, by the sound of things, her husband's whole demeanour has changed. From a practical point of view (cost, using up annual leave etc) a 2 week trip from which she is excluded isn't something which many of us would be too pleased about irrespective of the reason behind it.
I do feel awfully sorry for any child in this position and I am not suggesting at all that her father should pull back, but I think HE also has a responsibility towards his current family and he should be far more open about what's going on as he gets to know her. Maybe RELATE counselling for BOTH of you would help ? ..... I can't help feeling that DH is coming across as a bit selfish, ignoring his daughter in the 1st place, thus creating this "problem" and now, excluding his wife when, understandably IMO, she has a vested interest in what changes this new family member might bring about.