A.A.
Ah yes the tummy ache. I have a tummy acher and headacher. Usually when she does it (she's 12 now) it's because something is going on at school that is upsetting her emotionally. Although in the beginning I think it was due to drinking chocolate milk with lunch. I would check in to see if everything is going OK at school and when the tummy ache happens if there is something that could be causing it diet or exercise wise.
I usually tell my daughter to go back to class until the next break and if she still feels bad she can come home. She usually stays in school.
Hope everything's OK with your sweet girl.