Re: Vent about MIL
Look puzzled and say "Why on earth would I give her an inferior food from an inferior container?". Look at her with the expectation that she'll give a rational answer. Try not to smirk when she stammers.
Or simply "Why on earth would I do that?". Wait for an answer. If she answers with "So you can have some time alone....so DD can stay with others so you can have a break (which is probably the REAL issue....she wants the baby for a while without Mommy)...so baby can learn independence", say "Childhood is too short. We're not in a hurry". Smile.
Or, if you can be in a situation where there are several people around, including your MIL, make it a point to be in a conversation about your baby with someone else so your MIL can hear. Make a general statement about how you just don't understand why anyone who didn't physically have to would choose not to breastfeed, and how using bottles doesn't allow a child's mouth/teeth/palate to develop properly. Say how proud you are of yourself for taking on the challenge, and how sad you are for friends who get flack from family because they don't give bottles. Say it all in sincere tones.