I had this with my youngest she broke me and it took a very long time to heal. Things you must do:
practice saying, please don’t talk to me like that, then walk away - do not engage. If she follows say I am not discussing this with you while you are being so disrespectful and refuse to engage. Even if it means going for a drive.
Around this time I was also expected to be the emotional dumping ground for everything else going on, constant phone calls to this day whenever the phone rings I panic with a what’s wrong now feeling.
you need to be less available, swimming and scuba diving works well as the phone doesn’t work under water. Make sure you have something on several times a week where you are completely unavailable. (This works twofold as when it’s all over and they’ve gone you actually have a life so empty nest syndrome doesn’t impact)
my DH always thought I was over exaggerating until I stepped back and he had to deal with it. Make sure you call him out when she verbally attacks him.
Also with regard the elderly parents. Have you looked into carers allowances etc, that way they can fund things like cleaners and gardeners taxis to hospital appointments etc any little thing that takes the pressure off you.
It does pass.