I have a beautiful 10yr old stepdaughter. She has always had behavioral issues though (lying, hitting, cussing, stealing and sex issues) With lots of patience, her dad and I seemed to be getting these things under control. She tested the waters at first with me, but our relationship really blossomed over the last year.

Her mother is very possessive of her. Dresses her very provocatively, puts makeup on her, dyes her hair, etc. Mom has even had this child lie for her when she does things her husband doesn't know about.
This week, we received word from 3 people at school about failing grades, bad behavior towards teachers and peers and a notice that she has had a second offense on the bus. My husband tries to call her and her mother refuses to punish her because she says "she already had to hear it at school", why drag it out at home. Mom enrolled her in after-school activities and has not been restricted from those either. In other words, no punishment, no consequences. The school is looking to my husband and I for help because she is out of control. Mom has even told her that we are too "strict and boring" and has offered after-school activities in leiu of coming to see her dad for visitation for the past 6 months.What do we do if Mom won't be on board as a team to get her back under control?