Something I'd always laugh about was when people who hadn't had teenagers yet gave me advice. They'd talk about the total control they had with their lovely 10-year-old who just made the honor roll until I'd want to scream in frustration "Just you wait til she's a teen, then come tell me about her!!!"
Well, I had total control when they were 10 years old also, and you can even sometimes control the schoolwork and grades at that age too.
Everything changes when they become 13. If they don't like an after-school activity or a sport, it is impossible (in my view) to make them participate. I wouldn't try if they didn't have an interest. Waste of time and money while they think of every excuse in the book and fake sick to miss practice.
I also feel it can be damaging to keep them isolated. The phone and the computer are pretty much the digital age place to hang out. Look at us, we're hanging out here. I'd go crazy without my internet friends, so I wouldn't deny my teens the friends and support they get that way, even though it may seem new to you. You just have to monitor it, especially the pictures.
At 10, along with elem. school, you can meet almost all your child's socialization needs. But not at 13 and beyond. They actually need friends and support from people their own age. And you can have something to say about who they hang out with to an extent. Just be aware that from now on, you aren't going to be the only one making decisions. She will too, and she's going to carry some of them out against your wishes. She'll make some mistakes, and sometimes, she'll go completely against your beliefs and everything you taught her. Try not to blame yourself. If you love her and you did the best you could to bring her up right, she'll more than likely come out the other end OK.
A great book for moms with teen daughters is:
"Get out of My Life, but First Can You Drive Me and Cheryl to the Mall?"
It is a practical guide to teen girls by a really funny parent and psychologist. You would love it, fast and easy read for a stressed parent.
Good luck, sweetie. I'm on my second teen, a boy, now. Whole 'nother animal!