When did her disrespectful behavior start? When she was a child?
I agree - my heart would be broken. I also don't think these things happen out of the blue with no prior history.
Maybe treating her like a Queen made her feel she is/was entitled to be treated like a Queen.
She's an adult - I'd do nothing and see what happens next. She might reach out. She might not. You need to find peace for yourself and your husband, with or without her, whatever that takes.