why is she looking at me like I'm a bad mom when i just want to protect her?

my daughters 5 years old her father and i split when she was just a couple of months. he wasn't the worst man but our relationship was toxic. shortly after I meet my husband that I now have 2 boys with, my daughters father hasn't had a stable home since we've split so even tho he managed to call her everyday theres also been times were he won't see her for months. he just came back a little less then a month ago after being gone for 6 months and is now living with his sister. since he's came back shes asked to stay at his house almost everyday at first i thought why not she just misses him but then i started to see a change in her attitude. she's become aggressive, demanding, bullying her brothers and all her manners are gone. so i sat her down and also spoke to her father and told them i thought only sleepovers on weekends was best for now. well after having that conversation with her, she went to her dad and told him I didn't want her sending time with him ect, ect! long story short she now wants to move with her dad obvisiouly I said hell no but now I'm looked at as the bad guy and being told i should give him a chance 😠😠😠