I think there is a blessing of them developing whilst still at Primary school, my Dd hasn't been mortified by talking about BO, periods and body hair whereas at secondary I think she would. Although she has said because I'm a science teacher that teaches these things to lots of other people it's not as weird.
Once she commented on her leg hair I taught her to shave her legs safely by running her a bubble bath, asked her if she wanted to wear a swimsuit but she didn't mind and then gave her the shaving cream and razor and taught her how to do it and what not to do. Told her there were other options and she didn't have to remove her body hair if she didn't want to. Nobody had this conversation with me and I used to use my dad's razor are cut myself several times.
Periods, started off with disposable teen ones we had in the house, had a discussion about environmental impact, she tried reusable - doesn't mind those but a bit thick, just bought her period pants from Cheeky wipes to try. Again I don't think we would have had these convos if she was older.
When she developed BO, and boy did her pits stink to begin with I bought her scrubbingtons deoderant it's purposefully designed for adolescents as they can be really smelly whilst their hormones settle down but without as many chemicals as the likes of Mitchums.
We were able to have very sensible conversations about these things without the teenage embarrassment she probably would have shown by 13. I know having those conversations with my parents as a teenager I wanted a hole to open up and swallow me whole but because they are still in primary school they are still accepting of our guidance.