I am a Bio mom who's in a custody battle with the father who's getting married. From your description, there are a few things I would be concerned about:
1. It should be your husband, the father of the child, who stand up for the daughter. You are his helper but, sorry to say, you are not her parent. I know that there would be bad mom, there are wonderful wonderful stepmom; but I got to tell you the best dad (or the best stepmom) in the whole world is still not a mom.
2. You did mention a lot of things the mom is doing unwisely. My question is: What have the father tried to ease the problem? Were there communication, negotiation, etc.... Because as it usually goes, mom would have a whole list of complaints too. Try to work it out and leave the court to the last resort.
I said these because from experience, you do not want to go to court unless it's absolutely necessary. It feeds a bad circle of hurting each other. Trust me, your hubby would be hurt no matter what. The court would make you guys mediate first anyway. The emotional drain and financial drain is incredible. So unless the child is physically or emotionally harmed, don't sweat the smaller stuff.
Often times parents value different set of skills. One value structure and responsibility, another value creativity and freedom. Kids can learn from both of us. Think long term. Will what happens now hurt her when she's 25? Well....I got to go but good luck to you!!
Try work it out, try parenting classes together, try co-parenting class together, they do help us understand and the kid would benefit.