I agree there are so many unknown about this situation. I just requested several books from the library to see if reading any of them will give an good suggestions and also a couple books about disassociative disorder to see if I can try to better understand her condition. If I recall in previous research, estrangement is more common with those with mental illness. Will continue to seek information to better help and support. I have thought about reaching out to the mother to see if she know anything, she will not share any info with my friend, if she does know anything. As I mentioned, this situation is just so heart breaking and to see my friend suffering so much and missing his daughter is difficult to watch. It is definitely taking a toll on him something needs to change.
Really appreciate all the kind words and support.