So far, I've seen several potential issues mentioned in this thread that some people consider trivial and some people consider vital:
* Happy Meals (junk food in general)
* Meat (ethically ambiguous foods in general)
* TV (an extra hour thereof, any at all)
and then some issues that most of us consider vital:
* don't hit the kids
* don't let the kids CIO
* don't drive the kids around without properly restraining them
The OP feels she has an issue with her MIL being disrespectful. That may well be true. The MIL seems to feel that the OP is hypersensitive in the matter of a child's hypothetical future diet. That
may well be true, and MIL may feel disrespected by that, depending on how it's expressed in social situations. Since the child in question is only four months old, probably all involved are going to find their positions shifting and changing in the next few years. The fact that it's even being discussed at this point lets me know that both the OP and the MIL are not dealing with their difference in the friendliest, most respectful way possible. I have no problem following food rules when I babysit a child, but a first-time mom of a 4 month old who is listing out her Cast In Stone beliefs about what her child should/will/can eat a year or two or three from now? I think that person is in for a reality check about the level of control that one person (even a mom) can usefully and healthily wield over what is chewed and swallowed by another person (even a toddler. Especially
OP, you need to decide if it's more important to have dietary and other non-safety-related restrictions respected, or for your child to spend time alone with Grandma. (I can see either answer being the right one for you, depending on your specific beliefs about food, family ties etc.). Then you need to ask your husband what HE thinks, and then the two of you need to arrive at a compromise you can both live with. If he wants his mother to quit the passive-aggressive spiel, then he should tell her that. If he wants his wife to show some deference to his mother in non-life-or-death stuff, then he should express that as well. You can't begin to work out a solution among parents until both of you are being really honest with each other about your priorities. And you certainly can't deal with a MIL issue until both of you are on board with a solution and presenting a united front.
I feel like this comes off as me not supporting you in eating vegetarian yourself and in feeding your child vegetarian foods. I DO support that. But you are the only vegetarian adult in her life, and if you want other adults to have important caregiving roles, then you may want to consider letting go of the control a bit. I'd be saying the exact same thing if you were the only TV-free adult in your child's life. I happen to be the only adult Jew among my children's local family caregivers, and you know what? They watch Rudolph. With my MIL.
Letting go of a bit of control doesn't mean - "fine, give her meat, I condone it." It might mean "fries and chocolate milk are OK, but no Nuggets please." In the nearer term, it might mean buying some non-meat Gerber with a high protein level listed on the label and bringing it along in the diaper bag when Grandma babysits. Show that you, too, care about protein
If your husband was happy and loved and safe in his mother's house, your child can be too. It might be best to stop counting the years until she "goes senile" and be grateful that she's still got it together and your children will have good memories of her. You don't have to like her. But your husband loves and respects her, and his children should as well. Right now, before your child is old enough to notice any friction, is the time to figure out how you can engender that without making yourself miserable. I don't know waht your answer will be, but I do
know that your resentment level is sky-high right now, and that something needs to change.