Hello Jeannie-
You're in a tough position, because you are not just dealing with today's behavior, but setting the standard for future behaviors. Right now, you guys have a good relationship, which is great, but you need to "tread lightly" to keep that relationship and open communication as the teenage years start.
If you are too harsh, your child's friends MAY use peer pressure for your daughter to break the rules, "your Mom will never know if you..." On the other hand, staying within your family values is also important, so you cannot be bullied to stray from what you believe in.
I'm a parent coach, and it's important to me that parents and children create a relationship based on respect and honest, because with this base, children are more likely to come to you when they are introuble as teens, (I used this system when I was a Nanny, my former charges are now 12 & 13 and I get calls all the time asking for advise about___. It makes me happy to know they will not try to handle big issues alone).
I advise parents to create household rules WITH thier children along with written consequences for those rules, again, the child helps with the consequences. This way the child is a part of the entire process and not only aware of the rules, but is more likely to follow them.
Sit down with your daughter, have her tell you honestly what she wants to do & why. Then tell her honestly what you what and why. Next create the rules you want followed together, try to provide her with some freedoms based on what she wants. She will really appreciate that and comply better.
Next, talk to your daughter about ways for HER to handle when her friends can do something you don't want her to do. It's hard, (I know, my Mom was very strict through my high school years), to tell your freinds, "My Mom won't let me" kids feel like a baby and then start trying to find 'work arounds' to the issue.
I also suggest you think of ways for your daughter to experience situations like her friends while staying with in your comfort zone. Maybe you go to the mall with your daughter, give her a cell phone and you go to one store & your daughter & friend goes to another.
I hope this helps. Children at 11 are still children, but so often allowed to act like older teens/adults. Parents are thrown in the middle, and it's never easy!
R. Magby