My mouth is still hanging open at the bare-faced cheek of it. I would want very much to put my side of it to my aunt, so I didn't get tarred with the fall-out from your cousin's staggering behaviour. But I think it's best to let sleeping (female) dogs lie, and keep well out of it. That is all kinds of crazy.
I would send a card, a gift if you wish, and let it go at that.