I didn't tell her to cut her parents out of her life.
I said she should hold out for an apology and a recognition that they were very wrong to do what they did.
Advising someone to let people walk all over them doesn't strike me as being particularly wonderful.
She's currently going to let the relationship die a gradual death.
I might do that if my parents meant very little.
Or I might have the row and see if we could get it sorted.
But asking someone to pretend that people who behaved so appallingly are sorry is daft.
Her feelings, and her husband's feelings, matter.
Her marriage matters too.
How would she feel if her husbands's parents attacked her in that way and he expected her to carry on as though it was completely normal to ambush people like that?
They were way, WAY out of line.
Sometimes you need to stand up for yourself.
IMO the day your Dad tells your husband your 4th child is unwelcome, you are unstable and he is a bad husband is the day you draw a line.