My own children, who are slightly younger than this stepdaughter paid for their own weddings, because their in laws could not afford anything. When my younger son, who was 25 when he got married, went to the court house, DIL insisted on having the "country club" reception 9 months later. Although it was lovely and done on a budget (8K), why should my son have to spend his savings on this? It was all for the benefit of her family, who can't afford anything. We paid for the dinner the night before (Chinese food). We gave them the gift they asked for, which was actually cheaper than we would have spent if they hadn't asked for this. This DIL reminds me slightly of your stepdaughter, Dogmamma... moody and slightly unappreciative. It makes me feel like my son is seen as a "catch."
My older son was 28 when he got married. This DIL has very dysfunctional parents and although we offered our home to have a small reception, she didn't want her parents to interact in any way with our friends or theirs! She was right, although at the time, I was disappointed. They got married by a JP I know from our synagogue and then we went out for Korean food with her parents. I haven't seen the parents since! We have done many nice things financially for them, not because they ask. They deserve it. They are warm and friendly, socialize with our friends, who have known my son since he was 8. It's exactly the way I envisioned a relationship with an adult child. We don't see them all of the time, but we are close. For example, we offered our son the birthday present of a tune up on the Serotta we gave him (it was our other son's racing bike, sitting in the shed). He's had it for 2 years and it needed work. Well, wheels, brakes, chain, bottom bracket, tires, bar tape, etc ended up being quite a sum, but DH enjoys doing the work and again, he deserves it.

I wouldn't go overboard on the gift in this case, Dogmamma.