Thanks guys. Poor kid feels so let down by her nan. She's used to her mother letting her down, but she's the only grandchild for goodness sake. She made her wishes clear after her nan went to visit her mum in rehab - boy she was angry about that - and my MIL called up & as i was the only one home I had to speakto her. She told me she didn't like being told what to do & that she didnt have a choice, because if she carried on seeing SDs mum she would lose her son & granddaughter. She said she felt like she was being treated like a child & that SD had no right to forbid her from seeing her mother. I explained that SD felt she was betraying her & that she should be loyal to her, & that she did have a choice, just as SD had the choice of accepting her disloyalty or not. She hung up on me, but text SD later promising her she wouldn't have anything to do with SDs mum again. My husband text SDs mum & told her what his mother had promised and why, so for her to completely disregard her daughter's feelings is & gloat is, I think, cruel. I know we have no control over their actions, and we are contemplating blocking their numbers from our phones & just let them get on with it. It sucks though, big time.
There is no alateen in our area, but she has weekly counselling.