I have read all the posts. The comment about the baby being with the girlfriend, but not the little girl, prompted me to ask if the gf and ex actually live together. It’s also reasonable to ask why, if the gf has been in the child’s life since she was born, and makes all the decisions about her, the child is not allowed to call her ‘Mum’, or the new baby ‘sister’, is it not? All any of us can understand about the family set-up is what the OP tells us. I have asked if her ex knows of the visits to the birth mother but she has not responded to that.