OP should not put her child somewhere that she has a gut feeling is bad...it doesn't matter if it's the Grandma! What if her "fail" is driving her without a car seat...what if she gets in a wreck? "they didn't use car seats when mine were little and they are just fine!!!" You wouldn't believe how many Grandmas believe that. What if she gives her honey and she gets really sick? There are so many "what ifs" that if she "fails" like that can't be taken back. Unless the MIL can prove that she respects the OP and the way she wants to parent she doesn't deserve the privilege of watching LO. It's not on the OP...the MIL has SHOWN her she won't listen, why are people telling her to ignore what the MIL herself is showing her?
And some people sacrifice babies in Satanic rituals, yes, you can never be too careful!!
Or... maybe you can be too careful. As far as I can see from this thread, the only things MIL has done in opposition to the OP's wishes are
- pick up a crying baby
- suggest that BF is better than FF
- suggest some Weetbix in formula at three months
- did some washing without being asked
I don't know but this doesn't exactly sound like the sort of reckless woman who might drive around town with an unsecured infant. So it's kind of hysterical to suggest that she is potentially a physical danger to the child. That, to me is the sort of helicopter approach that has resulted in the bridezilla/momzilla culture that you see on TV these days - the attitude that 'It's my day/It's my baby and therefore ANYTHING I say goes', no matter how irrational/inconvenient to anyone else/damaging to relationships.