I couldn't read and not post, even though I'm not sure I have anything useful to say. I definitely think you should see what the dr/HCP has to say about it.
When I was in third grade (so 8 or 9, I guess) my skin starting breaking out. I clearly remember my mother saying, in a tense worried voice, "But you're too young for this!" and I really felt like it was something bad I had done.
Because of this, it really struck me when I read an article a few years ago (don't remember where, sorry) saying that the early stages of puberty for girls normally do start much earlier than we had previously thought. It's a complicated process and takes a long time; menarche and growing breasts are just parts of it.
On the other hand, puberty also starts earlier with each generation.
And then again, there is evidence that environmental factors (endocrine disrupters like plastics and whatnot) are causing unnaturally early puberty in girls.
I don't know the answer, but I did want to let you know that it may be perfectly normal, and just something we weren't aware of before, but that you should definitely follow up and share the information you get with your daughter in an appropriate way. If you have noticed changes in her body, changes are good she has noticed them too, and she needs you to help her understand them as good and normal and just part of who she is, part of growing up, and not something that is "wrong" with her.