Well, personally, I would go. It's important to your husband, and who knows, maybe having a little one has helped her grow up a little.
As far as presents go, the offering to help write the thank-you list was a brilliant suggestion. BUT even if you write it she may or may not get around to writing them. Some people are just bad about that kind of thing. Really though, the present isn't for her - it's for the baby - and you don't really expect *him* to write you a thank you note now do you? :)
I try to focus on the joy of giving (even if I am giving in to a "pressured" give) rather than on my own need to get something (like a thank you) out of it. Knowing I did something nice is the best reward anyway (as well as instant gift-giving gratification!) and seems to keep me feeling better about the whole gift-giving thing than basing my feelings about the event or person on whether or not they write me a note or give me something back.
I'd say go for your hubby, and who knows, maybe with you being the kind person you are, you will become the woman she turns to for advice to get that world-view of hers turned back around!