My MIL keeps saying my kid isn't normal

So she's got this compulsive need to keep telling me, my SO and my son that he's not normal all the freaking time.

He does something silly, and funny and she'll say "Gosh your child isn't right in the head"

He's just started to learn how to walk and she spent her entire time here yesterday telling my SO that he's not walking right. And it's not like she's joking, she says it like she's serious and thinks we need to take him to a dr.

He's fine. There's nothing wrong with my kid. He's advanced, he's strong and he's very clever (Yeah I'm biased but who isn't and it's true)

It bugs the crap out of me because we found out I was pregnant late, and I was a smoker and casual drinker but I stopped as soon as I found out I was pregnant, but it feels like she's trying to find something wrong with my kid all the time so she can blame me.

And I'm not being totally paranoid, I know she talks shit about me to my SO's sisters and to him because they've all told me. She likes to make "jokes" about everything when they're criticisms and then gets upset and storms out if you call her out on her bullshit.

That stiff I can accept to a degree, talk shit about me all you want, but don't keep telling my kid that he isn't normal so he grows up thinking something is fucking wrong with him when there's not.