I think the best thing u can do is sit down and have an open and honest discussion with SD. She’s 8 and I’m sure she’ll be able to tell u her view etc. To me, it sounds like BM is trying her luck and unfortunately as u or her dad haven’t seen her, u will jump at the first opportunity because it isn’t SD fault that mum stopped contact. However I would contact mediation, because they will get something in place again before BM stops contact next time for whatever reasons. It can be a legal document that would hold up in court. Randomly withholding contact and saying it’s for the child’s best interest raises flags for me. SD could be acting out because she hasn’t been able to see u. Just sounds like BM has weaponised her child. It’s awful x
I wouldn’t have your bio child near your SD at all whilst these claims by BM are happening. Funny that all of a sudden she wants contact again. It’s all a game.