Maybe she says she doesn't want to babysit to have you say, but we would really like for you too. YK like inflate her ego. Tell her a bunch of ways it would help you guys out. I am unsure and those comments would be hard to deal with.
I know exactly what you are going through. Not the crib issue, but MIL is the most passively controlling person I know. Everything has to be her way, her time, and everyone just listens to her. I just really found that I lost my DH's support when I started to complain about everything. I got him on board when what I was complaining about had hard evidence of why it shouldn't be that way. If I was in your situation I would explain to my DH how unsafe a used seat is, show him plenty of videos, and insist that they destroy that seat. I would make him broach the subject with her, bc than I wouldn't have to deal with her explaining why it is okay no matter what you say. And then with the smaller stuff I would vent like crazy to friends, my mom, and anyone who would listen why I can't stand my MIL and let if go, or at least not bring it up to my DH
I really think you are right about it being about your relationship not really the crib. My MIL insisted on holding DS the second we walked through the door. If I said he needed to nurse she would watch me like right over my shoulder and the second he stopped sucking she would annouce "okay grandma's turn to hold him" She would try holding him even though he was wailing, and say things like "oh Grandma loves to hear you cry " and when I would take him she would get VERY upset and say "oh you were fine I don't see the problem." I would get so worked up inside about stuff like this and I would think of what I should do if she does A or B and I should say C and D but if she did E and F then I should.....I would stress myself out at the mer thought of seeing her and be on edge any time I was around her. When my son was born he picked up on my uneasiness about her and would literally scream everytime she looked at him. He is now just starting to feel comfortable with her, mostly because she leaves him alone to see the new baby
I don't know your MIL, but the only way I can deal with my MIL is to remind myself that she really cares about my kids and has a good intentions (most of the time ) Since my children are soo important to me, I don't want to ruin their chance at a relationship with a grandparent that truely cares about them. So sometimes I bend a little, and other times I really stick to my guns. I think it is important to do both. It really does get better, but prepare for it to get much worse when the baby actually comes and that I what I meant by my post. Sorry if I offended you in any way, I just know how rough it can be for you, DH, and your lo. Good luck.