I work at my kids' school. I deal with this ALL the time, everyday.
#1, kids this age don't know their body's cues.
Thus, they don't know "why" their tummy hurts.
So try and teach your child, about why a tummy can hurt. I taught my kids about their body's cues, from when they were toddlers.
The reasons for a tummy ache are commonly:
1) they have gas, and need to fart or burp. Gas pains do cause pain. If this is the case.
2) nerves, but this is not common
3) they have to go to the toilet for #2
4) They are hungry and don't know hunger cues
5) Or if at lunch or after lunch, it is because they eat too fast, or are too full. And they don't know their body's cues for being "full." Or were not taught about their body's cues for "hunger" or "fullness."
6) They are sick or ill. Thus this warrants a trip to the health room.
The Mints, are not a cure. She probably just wants the candy.
And as you said, she is running around like normal, and the tummy ache does not impede her, at all.
As I said, I see this everyday, per kids, especially the younger ones.
And these are the reasons, for a stomach ache.