This is really a difficult situation for you. I can’t imagine what you can really do. On hand, you want to do everything you can to help make her life a good one... on the other hand she is a responsible adult with her own choices to make.
My H was in a bad depression for a while and it was really hard for me. It’s hard to be happy in a home that has a heavy gloom over it. So I got out of the house a lot and left him to do his own thing. He muddled about the garage and yard with his projects. He eventually pulled through but he does tend to have a depressed nature and we clash at times when I try to get him out of it.
What do you think helps her the most? Talking about things or being left alone?