I'm sorry for the situation
I think it is normal to have a hard time and to cope with feelings of rejection
She's an adult, that's true. Maybe her inner child feels betrayed or messed up
I'm not sure of this but it could be a good idea to give her a chance to open up more with a psychotherapist, someone kind. maybe you can carry her there

I'd say your father should behave a bit better. But I imagine how complicated is the situation and how difficult it is for you to talk with both of them