MIL knows better than doctors

Curious to know how others would react and feel about a MIL like mine. There’s a long history of her over stepping boundaries and being disrespectful and I mostly bite my tongue to keep the peace but she crossed the line yesterday. My son has had to see a dietitian and a gastroenterologist who we are very lucky is top of his field due to issues opening his bowels more or less since birth. He has advised we go no dairy for 2 months and is also doing an examination and biopsy under general anaesthesia. As if we don’t have enough to worry about MIL has to put in her two cents and “isn’t convinced” that the specialist knows what he’s talking about. She tried to give our son food with cheese in it yesterday and started pushing back when I said he couldn’t eat it saying she couldn’t understand their logic and “a little bit won’t hurt him” He also has glasses but she’s also doesn’t believe he needs them because “how can they even do an eye test at this age”. So if they ever mind him they make zero effort to get him to wear his glasses (which he should be wearing at all times). I’m at the point where I can’t stand being around her and she’s affecting my mental health. They live ten minutes away and are constantly trying to impose. She turned up at our house this morning and asked does she need to come over and water them EVERY DAY. My husband agrees she’s overbearing but is scared to stand up to her and just wants to keep the peace. I think he thinks I’m overreacting but I feel like most people in my position would be losing it at this point too surely. Thanks for anyone who’s got this far just needed to vent and also hopefully hear I’m not going crazy and that she is in fact unbearable 😭