My 16 year old daughter has the "Cinderella" syndrome. What should we do?

Basically, I feel it's unfounded as the step sisters don't live with us, don't visit, and simply have minimal contact at all. The daughter got in deep trouble, then showed major disrespect over more than a weeks time and as a result, she lost her car, cell phone, job, and IPod. She was grounded for a week, but that was because she had let her grades slip to 2 Fs and a D. She contends that we are too stricked because we won't let her stay out until she's ready to come home (we have a curfew of 9 on school nights, 11 on weekends) and we tend to tell her who and why we disapprove of some of her friends (1 thinks is a game and is now with child, another was arrested for drugs and , another treats her parents as if they don't exist, etc). In talking to Social workers and co-workers, they all feel we're doing the right thing. This new problem (the Cinderalla complex) seems to have come out of no where. Should I address it, or walk away each time she brings it up?