I don't think there is one "right thing" here - nor do I think you are particularly obligated to do any one thing.

From what you've said:

1) Helping will be a financial stress for you;
2) You have helped maybe more than would be "required" with her education (without thanks);
3) Your DH doesn't feel strongly;
4) You want to do the "right thing," but don't really *want* to do what you listed because it's too much;
5) She probably doesn't *need* the help unless she goes overboard with a wedding.

I think I would show up for the wedding, and give her a $200 or so (or a gift of equivalent value). I certainly don't think you are in any way obligated to do more.

Of course, this is just my take and YMMV. I expect that hearing others' opinions might help you sort out your own.