A.S.
My first thought... talk to her. My daughter is only 7 but she talks to me about her feelings and why she's having them.
I know when I was in school, there were a LOT of issues I was dealing with including puberty (I was only barely 10yrs old when I started). If my mom would've taken the time to listen, I probably wouldn't have been so angry and frustrated. I remember those times in my life very clearly. It was confusing and unless the adult takes the lead on the conversation to start, the child won't say anything and keep in bottled up. I make sure I sit and have chats with my daughter. I answer all of her questions the best I can and let her know if she's feeling something, whether it be anger, sadness, frustration, happiness, whatever... She can talk to me about it.
For example... There was one time that she told me that she was mad at my mother and went into detail of why. And she asked me why she is the way she is... It was a rather deep conversation between me and my daughter (she was 6 at the time. now 7) and I answered everything the best I could, but was honest about everything. She tells me everything. I hope it stays that way.
Good luck!