It really does sound like her mental health isn't great right now. Maybe you'd both benefit from her seeking some form of treatment or taking care of her mental health in other ways. Does she have a support system other than you that she can vent to?
I've suggested going to a therapist, I might go myself if this becomes too much for me.
She has a complicated family, but she's close with her sisters and has good friends too. She was supposed to see them soon, but I don't know if she'll go