Hello,
Thanks for posting your query.
Chest pain in kids this age is very often due to minor conditions like costochondroitis ( rib pain) or muscle pain due to overexertion or Problems like anemia or hypocalcemia and rarely due to cardiac conditions .
However if the pain has lasted for a long time or progressively increasing in severity or frequency then it's best to get her evaluated by her pediatrician and get baseline investigations like blood counts ,X-ray and ECG .
As of now it doesn't appear to be worrisome and is most likely a bone pain or muscle cramp which can be related to exertion and which doesn't need any specific therapy .
However a routine examination by her pediatrician would atleast rule out any possibility of serious illness and relieve your anxiety.
Hope I have answered your query.
I'll be available for any follow up queries.
Wishing her good health.
Regards

---