So put no thought into anything for MIL. She has given you a golden get out of buying gifts for her forever card. She gets NO gift for any occasion and, maybe just maybe, a card. But make it a very generic card, e.g. simply a Happy Birthday card from the dollar store without mentioning the word mother. Christmas cards, the box of generic cards from the dollar store would be nice (although I must admit I have found some cards I absolutely loved there). Mother's Day, no card at all. She's not your mother.

Stop letting MIL live rent free in your head. Maybe counseling would help you evict her.