I started at 9. They were proper, heavy periods from the start, but irregular. I would tell her class teacher.
I felt so lost and confused by it all. Nobody else I knew had started. I don't remember explicitly being told not to tell anyone, but I think I was, or at least it was implied, as I definitely felt as though I had a secret I couldn't share.
I think my mum thought I was so young and dealt with it by only telling me what I really needed to know (I guess out of trying to protect me from all the details). This was the absolute opposite of what I needed.
I needed to know exactly what periods were and why they happened. I needed to know that what was happening was normal except I was younger than most people and that all the women in my family and all the women I saw on the street had them. I knew about sex but didn't understand the link between periods and reproduction.
I'd been told about periods but not puberty and was baffled when I got pubic hair and nobody else did. I was baffled when somebody used the word puberty as I had never heard of it. (This is after having pubic hair for over a year). I hated getting boobs and hips and thought I was fat. I wasn't - I was just more developed and so my body wasn't as small and childlike as my peers anymore.
There were no bins in the children's bathrooms so I was allowed to go to the teacher's bathroom but I was scared that one of the other kids would see me and tell everyone (assuming they'd caught me being 'naughty'). I was also worried that another teacher might not have been told I was allowed in there, or would forget, and would tell me off. I would have been too embarrassed to explain. In hindsight, I would have only had that problem once as my mum would have torn them a new one but I didn't want to risk the embarrassment.
We went swimming with school and we were expected to change in communal changing rooms. As the only one who had gone through puberty in a class full of children who didn't even know about it all, this was extremely cruel. I wore pads so couldn't go swimming on my period but didn't know what to tell people so I told the other kids I was sick and then everyone would gossip that I was always pretending to be sick.
On the days it happened my mum would ring the school to tell them I'd started my period so couldn't attend swimming and a teacher complained to me that my mum kept ringing her and she already knew. I didn't understand if I was supposed to just tell her myself each time (mortifying, especially trying to do it out of earshot of anyone else) or if I was supposed to give her a wink and just not get on the coach. It all sounds so ridiculous and silly as an adult but I was a very confused as a child. There were so many aspects to navigating this new thing that nobody seemed to consider and everybody seemed to assume I just knew what to do.
I needed to know where to keep pads so I could subtly grab them. I needed to know how dip my hand in my bag and shove a pad up my sleeve so it doesn't bulge out. I needed to know about little tins or pouches to keep it up. I needed a skirt or trousers with pockets in ideally.
I needed to know how to fold tissue into my underwear in an emergency to last for a couple of minutes until I got a pad.
I needed to know what to do when I went to people's houses without a bin in the bathroom. (Please please everyone put a bin in your bathroom!) I was once chastised (not told off exactly but just shamed) at my grandmothers house when there was no bin and I wrapped it and brought it to the kitchen bin. Apparently this was the right thing to do but I wasn't subtle enough and my grandad saw me doing it. (god forbid! Not a man seeing a little girl throwing a big ball of tissue into the bin and guessing its a period thing).
I needed to know what to do if I leaked onto my sheets or underwear.
I needed it not to be this awful shameful thing. Or at least, if it was going to be shameful, I at least needed enough information and tools to adequately hide it away like everyone else apparently did.
I would avoid any talk of her being "a grown up / a woman / not a little girl anymore." She is a little girl. It's not periods that grow us up overnight. She was your baby before this happened and she still is today.
I hated that I was suddenly told I was a woman but my friends were still allowed to be children. Especially while I was, ironically, sat there wearing a big nappy thing which I felt like everyone could see.
Going through your first period at age 13, in secondary school, when all your peers are going through the same, when everyone knows what it is and probably talks about it and you're expecting it is absolutely words apart from starting at 10.
It IS so sad she's having to go through this early, and let her express it if that's how she feels. But try not to be sad in front of her and try not to let it make you treat her as older than she is. Yes her body is now changing and yes the hormones kick in which affects moods etc. But she's still only ten. She will not be able to navigate this as instinctively as a 13 year old with a peer group in the same situation in a school system more set-up for periods to exist would.