If it makes you feel better, I have the same issues at my barn. The only way I have dealt with her is humor.
A woman is constantly harping on me about my underweight, limping, head-too-high, pushing too much off the back quarter horse. Excuse me? He's a walker.
One day I had to move down to the box stalls because my horse managed to bang his eye some how which caused the pupil to constrict and he temporarily lost vision. I was given medication which dilated his pupil to keep him from freaking out, but he needed constant shade to prevent sun damage to the eye.
I am giving him medication, and she just barged into 'my' stall and asks if he's contagious. I said no, and that he will only be there a few days. She asks if the medication is for his weight. I wanted to say, "Yes.. I am putting medication in his eye to help with his weight, ma'am." but I just said no, that he hit it and it was now dilated. She grabbed a flashlight and put it to his eye and I asked her not to do that and that a vet had already seen it.
She then just starts pulling on my horses withers, shaking him around. He keeps walking away, and she tells me if I got a chiropractor out for him his withers would grow and he wouldn't be so down hill. Since I met my horse as a yearling, he was downhill and has had NO withers. They aren't going to sprout from a massage, lady.
She then starts pushing his hip. As trained, he steps away each time. She tells me he is sore in the hip and that is why he limps when I trot him. I was ignoring her at this point, saying I needed to leave.
She then starts SPOUTING about how she was a big shot trainer in Oregon. (Mean while, she has 2 six year old warmbloods she can't start to save her life.) She then tells me my horse is about 400 pounds under weight, and would be pulled from any show I put him in. I was just cleaning brushes at this point, ignoring her. She walks back up to me and tells me I should look up a diet for a Quarter Horse under light work. I look at her.. slightly dumbfounded. I informed her he was a Tennessee Walking horse, and she asks for proof! I kind of laughed and said I don't actually carry his papers on me at the barn, but that when I bought him he has Tennessee Walking Horse papers. She said "Oh, if that's what they told you. Those can be faked."
At this point I just left, and asked the barn manager to please get her out of my stall. She was still shaking my poor horse. After she was... evacuated, I told the barn manager what happened. It's now the running joke at the barn that my Quarter Horse is limping every time I gait him.
People will always try to act like they know more than they know. Most of the people with any knowledge value it enough to keep their mouths closed until someone is seeking it. Best of luck dealing with your person. Mine still hollers at me in the arena that my horse is underweight, limping, and unfit to ride every time I pass her stall.
"Putting pads on a gaited horse is like putting a mask on a beautiful woman."