How to help my bonus daughter

My husband and I have a blended family I have 3 older kids 17, 16, 10 from a previous and he has one we have one together. I’ve been active in my bonus daughters life since she was 18 months now 3. I have an awesome co parenting relationship with my ex. We do what works for the kids they want extra time with their dad no problem. I have plans for them on his weekend no problem we work together. Her dad (my husband) is a great dad and adores her and the time they have together. We have modified custody. 1st 3rd 5th plus two extra days each visit. She is her moms first and only child. Her parents had a very toxic relationship and still do not communicate well. Her mother accused every past partner of physical abuse. Bonus daughter obsessed over her mom while she’s with us. All she talks about is the things they do. If we say you are beautiful she says Katelyn(her mom) is beautiful. We say I love you and she says I love Katelyn. We say your dress is beautiful on you she says Katelyn got it for me (which none of the things she wears with us came from her moms). We always follow those comments with that’s awesome baby or some other positive reinforcement because we don’t by any means want to take away from her feelings towards her mom. Her mom also allows her to still drink from a bottle which we stopped allowing at 2 yo. When we go to pick her up she throws a huge fit but the moment the door closes she stops completely and starts playing. Her mom has now started saying she doesn’t want to come see us because my husband hits her. He has never hit any of the kids ever. I don’t know where this has come from. I’m starting to wonder if her mom is coaching her. We just want to help her grow any suggestions?