Another "oldie" at 42 who started menstruating by at least age 10. I wish I could remember exactly; but what I do remember is that 2 months before my 11th birthday, I was in the hospital for skin graft surgery. I did not have bathroom privileges. I was in an adult hospital and told the nurse I had my period. "No you don't," she said. She left me there and refused to get me a pad. A couple of hours later she came back, saw blood all over the sheets and said "oh, look at that, I guess you really do have your period!"
I still remember that. I can't remember when it actually started, but it must have been happening for enough months that I felt very casual about it (until that point, mind you). I'm hoping it wasn't even earlier than that, only because I've heard there's a higher chance of things like breast cancer in women who started menstruating young. OTOH, I've also heard if you start menstruation earlier, you enter menopause late; which in my case is good, since I'd like another baby.
As for the breast buds, I don't remember a time in my childhood when I didn't have them. They happened REALLY young and so did the other stuff, right down to the great big feet (now size 12) when I was a kid.
It WAS a bit hard; but I also had other things going on, like severe burns and braces, so I didn't need anything else to make me stand out.
FWIW, if it happens with dd, I don't intend to tell her she needs to change her clothing or wear a bra or anything. I'll try to find a way to let her know what options are out there and maybe that others might think she "needs" a bra, just to give her a heads-up so she won't be embarrassed. I don't know. I do want her to know she can still be a child when she starts to develop, for as long as she wants. I wish someone had said something like that to me. Just because I was menstruating and wore a C-cup didn't mean I wanted to be a teenager. I wanted to be a kid.