Hi everyone. I will try to be short with this story but I am looking for any guidance you are willing to give. Thanks in advance.

My best friend (female) got divorced after 25 years of marriage 2 years ago. She has 2 adult children and her marriage ending was no surprise....separated many times before. She has completely gone off the deep end. She has ended life long friendships and isolated her family, is irrational and at times delusional with her kids, ex-husband, family and friends. She has made some very poor choices that I never saw coming like dating and living with a child sex offender. Her moods change constantly. Sometimes for days she seems like her old self and then she changes to this person that seems like a delusional lunatic. I am worried for her and her children. Her children and others have expressed their concerns to me as well and I have tried to talk to her and have asked her to see a therapist but all it does is cause an explosive argument. I don't know what to do but I feel like she has a legitimate psychological disorder (no idea what) and I am afraid to do nothing.