Your daughter is a "Tween."
Tweens are from 9-12 years old.
Thus she is a Pre-Teen.
Do a Google Search on "Tween Girl Development." And many good articles will come up.
Yes, their hormones are getting tweaked. This is another major, age-juncture and time of developmental changes. Know that.
The "American Girl" book series is good. It is for girls this age, written easy to read and to be read by the child and the Mom.
Any book store will have it. It is a whole series for girls, per friends, body changes, behavior etc.
You said nothing has changed recently... BUT yes, there are changes. Because, your DAUGHTER is changing, developmentally.
They change physically and emotionally and mentally, at this age and at any age-phase juncture.