Such a sad situation and really tough. It's terribly important to be there for your granddaughter, a support and a place of sanctuary. But, her mother has to realise the damage she is doing her own daughter. I would seek professional advice if you are unsure of exactly what to do. I have friends, who's son got involved with a women with two children. She quickly had another two with my friend's son. Things were fine for a time, but both became heavily into drugs, and she an alcoholic When our friend's son tried to extricate himself from her, she threatened to tell the police (falsely) my friend's husband had sexually assaulted her purely because he was trying to drive his son away from her house and on another occasion she threw herself in front of the car as my friend was trying to remove him from the house, once again, after he rang her in a panic saying she refused to let him out. He finally managed to leave and had all four children removed (two eldest are with her parents, two youngest with our friends). Their son went to prison for drugs offences and only the briefest access to his children. The mother can see them once a fortnight, but often arrives drunk or drugged, so my friend refuses to let her in. The children do not want to see her. At the time, my friend was in her late 60s and her husband was 70. They had to become the legal guardians of a 2 year old and a 4 year old to prevent them going into care. They've had to sacrifice their retirement to raise and protect them. Their social lives have ended as all their friends are off enjoying the freedoms of their own retirement after raising families. I've told this tale to highlight how, when your son/daughter chooses a bad partner, can impact heavily upon grandparents. My friends will have full responsibility for the children and face coping with teenagers in their 80s, if they live that long.