My stepdaughter is out of control and its ruining my relationship, please any advise?

why don't you look at this situation from her point of view. She used to live with her mother and father in the same house and see them every day. Then one day her world is torn apart and her whole life changes. Now someone who she has not chosen as a friend and is in fact replacing her mother is telling her what to do. And she is p1ssed off. Every other adult in her life has a reason that they have authority in her life, Teachers, parents of friends, babysitters all have a legitimate reason to be authority figures. All except you. In her eyes you have no reason to tell her what and what not to do. So why is her father not fulfilling this role? I heard someone say that it takes approximtely the same number of years as the age of the child for the child to accept a step-parent as an authority figure in their life. Until that time their biological parent should handle most of the discipline.