She may be happier and thus acting out less. Don't let a colleague convince you this is somehow a bad thing. Teens often change interests and moods relatively suddenly and it's not necessarily a cause for alarm.

Maybe she joined a cult that doesn't allow girls to talk back.

Or she's probably just becoming more mature Don't let your friend turn a good thing into a problem. The best way to know what's going on in DD's life is to talk to her regularly. Be happy that your DD is doing such a great job. Not all teens turn into raging a holes. A lot of them are pretty cool.

Is she in love? That may be a good thing.
If things are going well in her life, she may have new-found happiness. How old is she? Maybe now she's sexually fulfilled.

Congratulations, OP, it sounds like your daughter is maturing nicely and in a way that is good for her. If the changes were negative (grades slip, constant arguing or talking back, new friends who were a bad influence, getting arrested for theft, drinking, smoking, drugs) then I would be concerned but it sounds as though your daughter is growing up and comfortable with it!

My teen daughter seems to have changed significantly within the past 2-3 months, but mostly for the better or in ways that are neither good nor bad. She's been much more responsible both at school and at home, more involved and enthusiastic in her extracurricular activities, and easier to get along with -- almost no fighting with her sibling and hardly any teenage drama. Some of her hobbies and interests have changed as well, but she doesn't seem to be into anything unsafe or particularly concerning.

I mentioned this to a friend the other day, sort of marveling at how quickly & suddenly DD seems to be growing up, and my friend (who has two sons both older than my oldest DD, so I tend to trust her experience in raising teens) seemed concerned and cautioned me not to automatically consider this a good thing. She pointed out that sudden behavior changes can be red flags for something going wrong in a kid's life. It wasn't like she was totally negative or anything, and she was happy to hear that things are going well for DD and our family. But her warning has stuck in my mind, and now I'm wondering if there's anything to it. I haven't seen any red flags with DD and none of her behaviors have been self-destructive, but maybe I just don't know what to look for.

What does the collective wisdom of DCUM think: do some kids just mature very suddenly, or should I consider the abrupt changes with DD signs of a potential problem?