Needing some help

My OH has a daughter from his last relationship before me. She is in kindergarten. She normally is very good and listens when she is told what to do. Lately her mom has been saying that she is misbehaving when she is with her and her stepdad. She is flat out refusing to clean up when she is told to or get ready for school in the morning. From what her mom has said she has tried rewarding good behavior taking things away and spanking because it has come to that. Her mom said the spankings didnt even phase her and the only time she listens is when her mom says she is going to call my SO. She has used that one so many times that daughter doesnt even take it seriously until she is on the phone with her dad.

We dont have this problem when she is with us because she doesnt test her boundaries with her dad, she knows what will happen if she does. He has never spanked her and has never had to. We punished daughter yesterday when we had her for not getting up for school when she was told and refusing to do what her mom and step dad told her to do. She cleaned up the house and took the trash out for refusing to pick up her mess of toys at her moms and she wrote sentences saying she will listen when she is told what to do. This isnt the first time we have had to talk to her about listening to them because she seems to have been doing it more recently. Im not sure what the cause is and why she is so defiant towards them and not us. Idk if it has to do with the other siblings she has over there because they do behave badly and dont listen as well and that seems to be from my understanding of talking to daughter part of why she does it too. Her explaination is always well "fill in name" didnt do what she was told and i didnt want to do it either.

By no means do we really care for her mom but we still enforce that she has to listen to her and her stepdad and grandma over there because they are the adults. So when we hear of these problems we take care of them. I talk to daughter to try to find out why she is behaving that way and my SO assigns the punishments unless he asks me to figure out an appropriate punishment. What can we do to help them out with this? Is there something we are not thinking of that we could be doing? Any advice or help would be appreciated.