14yr old daughter in trouble - I'm p/t stepmum trying to help

[Badgerette1]

First post: my partner's daughter has been cutting, drinking, excluded day from school, continuous detentions and now arrested for shoplifting. Dad struggling to know what to do, poor r/ship with mum who drinks and has own issues. I've been in dad's and her life for 7 years trying to provide safe environment every other weekend. Usual terrible divorce stuff: blame, financial probs etc but dad now able to have some conversation with mum, who regularly drunk and unable to cope. My problem is not being core parent, how can I help child without being accused of interfering? The kids have grown up with bad language, alcohol and lack of boundaries. Dad and I have calmer environment and some boundaries but live 30 odd miles away and there is a lot of defensiveness on both parents' sides so difficult for me to help. I have no r/ship with the mum, never met. My feeling is that the issue is not being tackled and the big loser will be this child.

[Badgerette1]

Thank you Maryz. All replies are helpful as it's all new to me so glad to listen to experience. I'm trying with DSD's dad to get him to help support her mum but whenever decisions are made they suddenly change, ie we were meant to have her this weekend but instead her mum has let her go to a party that she didn't want her to attend. It's impossible! I just worry the signs are there and something worse will happen.