If my husbands family, or anyone slighted my family, they wouldn't ever be around me again.
Only you can allow another person make you feel less than.
It is quite clear from your posts how lowly you are viewed.
She has continued on because she has seen that she can treat and speak badly to you and about you, your family, and you have continued to see her.
You should have told her the first time it happened not to ever do it again or she will not see you again.
Instead you have skivvied for her and the family for 20 years.
I'm not having a go at you.
I am being honest in replying to how you have been treated, in your words.
Your husband is a bully.
Lying to yourself now will not help you.
You are a bullied abused woman and both your husband and his mother are zero class people.
Stand up for your family and where you come from and don't let yourself be used as the arse wiper for a bully and his witch mother.
Let him wipe his mothers arse.
Spend some money on therapy so you can build up your self esteem.
I would be refusing to be around her ever again.
I would be looking at the math for divorce.
It is not healthy to swallow such awful behaviour for 20 years.
You deserve so much better, as do your parents.