I have a 9.5 year old dd who started getting upset over the slightest little thing at the end of last year. I never heard any reports of her being upset AT school and she was happy to go.
It was at home, if she was looked at the wrong way, if she thought the tone of my voice was a bit harsher than normal, the tears would start, she would run to her room and throw herself on the bed sobbing.
When I am doing something she will walk up behind me and hug me from behind and just stay there, she rubs against me and just seems to need to be close to me all of a sudden.
Last Sunday night we were messing around on the lounge together, started with her poking me, me poking her back until we were tickling each other over a tiny little bell. We were both laughing so hard and thought having lots of fun. Next thing I know she jumps up screams at me "you hurt me" runs to her room, throws the bell across the room before slamming her door. I was gobsmacked. I went in and asked her what was wrong and she said I had scratched her, there was no mark so couldn't have been that hard and definitely not worthly of that reaction.
I have noticed she has developed little breast "buds" over the holidays so am thinking it is definitely hormonal!
Hope that is the case with your DD. Could she be feeling extra tired during school term and that is making her emotional too?
So she sobbed for a while longer then came out of her room sat down and watched tv like nothing happened.