I'll be a bit of dissent here. How close are you to your cousin? Are you invited b/c it is just a large family thing where all the women are invited or do you think you'll have a relationship w/ this woman after? Call me cheap, but if I was not close to my cousin and was not going to have any relationship w/ this woman aside from her wedding festivities, I'd go no more than $25.
On second thought...ITA i think $25 is good if you barely know her!
My former boss gave me $15 at my bridal shower, and I thought she was being a tight wad!! But I think $25 is acceptable!