I haven't read all of the replies but here is my take on this..
I've seen Sex in the City, and most certainly agree that it's not approriate for an 11 y.o. child to see. Regardless of me not agreeing with this choice, I wouldn't turn it into a battle.
DSD was allowed to watch R-rated movies at her moms a lot earlier than our house. There definitely has always been two separate sets of rules, on some things we were more relaxed, on others her mom and stepdad. It is what it is. It will be a lot more damaging to the child to see two sets of parents going in a battle over a movie (or food, or bedtimes, or whathaveyous), than watching Sex in the City at 11.
I wouldn't worry much "my stepmom does this or that and is mean to me" talk. Are you loving and caring? Are you fair and affectionate? She knows the truth then despite what she tells her mom or what her mom tells her. There are many reasons for that kind of talk: she might be upset with you for having to clean up her room, she might be just trying to strike a conversation with her mom and knows that bashing stepmom will engage the mom. Why does it matter?
Who cares what the mom tells your husband? If he believes his ex's word over what he sees in his house every day, I hope you guys are looking for counseling, and the ex is certainly the least of your issues.
If your husband loves you, and you know you do your best with your stepdaughter, then things will work out. I know that things are easier said than done, but I am only giving the advice here that I have chosen to follow myself...
Stop worrying over what the mom says or thinks about you. DSD's mom used to tell my beloved dp that I'm not a good cook (heh), that I dont' know how to keep up the house, that dsd shouldn't be spending time with me, etc. etc. etc. None of that stuff matters at the end. Your own actions will speak a lot louder than her words. The sooner you choose to believe this, the sooner you will become happy family.
P.S. Kids know right from wrong... Even if they choose to say the wrong things at times, or make wrong choices, they come back to the place where they are loved and treated with respect.