Okay soo I’ve been a mom for 6 years ! I have a 6 year old and I have a 13 month old. From the start my MIL tries to tell me what I should and shouldn’t do with my daughter. For example: MIL thinks my daughter has a constipation issue ( my daughter doesn’t , brought her to the doctor for it) she’s eating whole food. She eats everything from fruits , veggies , pancakes to chicken and potatoes. Sometimes she goes poop 0 times a day to 3 times a day. MIL still thinks she has a stomach problem when it was discussed at doctors and my 1st daughter also pooped when she felt at 13 months old. All kids are different. She goes well my kids pooped everyday. I keep telling MIL that she’s on Whole Foods and milk , juice and all that. She tries to tell me what I should and shouldn’t be feeding her and it’s getting quite frustrating. I go to my husband about it and he just goes you need to just ignore her ( easier said then done) she doesn’t stop till you agree with her. I’m not a disrespectful person so I won’t get nasty with her but she only bothers me when it comes to the kids is when my husband is out of state for work. Does anyone else go through this ? How else can you handle it?
If ur husband isn’t going to say anything tell her to stay in her own lane 
How about, thankyou for your caring thoughts, have taken her to the Dr. Told she is fine and normal. OK.
“The day you pay for all her food is the day I let you pick what she eats. Are you gonna do the shopping or send me the money and the list? No? Then back off”
You need to sit her down with your husband and say “I understand that you’re trying to help and I appreciate it. I would like for me and my husband to raise the kids the way we want to raise them. I will ask if I need your advice/opinion or You can ask to offer advice. Unwelcomed advice or “my kids did this” remarks are not tolerated but we will take any welcomed advice into consideration but please stop pressuring me to give in to your advice or there will be consequences such as less visits or etc. I understand you want to help and we have been taking our child to the doctor and will be following the doctor’s advice when it comes to our child’s health.” You can add or take away whatever you need to and she will probably test that, so you need to put your foot down and give the consequences you set while reminding her that unwanted advice is not welcomed. You also need to make sure that your husband supports you and backs you up because if he doesn’t she may go to him and he will give in to her behind your back, which will cause problems in your marriage. I had to put my foot down on my family and my ex’s family. Now they let me learn on my own while respecting my wishes about advice.
You need to set a boundary with her.
I’d probably say something to the effect of… “With all due respect, this is my child, and I will parent and care for them the way I see fit. If I’m looking for your opinion and input, I will ask you directly. I’m sure you mean well, but I find it extremely insulting when you tell me how to parent and specifically, when you insist there is something wrong with my daughter despite me telling you there’s nothing wrong with her. I don’t think you realize how your words and actions are causing undue negativity and stress on our relationship. I can’t have you continuing to undermine and question my parenting and authority as a parent. If you value this relationship, you need to stop and give me the space to be the parent. Let me be the one that worries. You should be busy spending time and making memories. Not parenting. That’s my job, and I assure you, I take very seriously.” See how she responds. There’s opinions and then there’s overbearing. She’s bordering overbearing. And that is toxic AF to y’alls relationship.
Sometimes you have to be rude and put her in her place. If this has been going on for 6 years it’s time to tell her to mind her own business it’s your child and you’ll do the parenting and if you need her opinions you’ll ask.
It’s meddling and rude not paranoia. End the conversation immediately by telling her these things aren’t up for discussion.