There are many structures in the center of the chest which can produce pain. It need not be from heart always.
It may arise from bony structures like sternum
and the adjoining ribs or from the food pipe and stomach or from pleura
that covers the lungs or from wind pipe.
Have her examined by your Pediatrician
to find out the cause.
Since you say she has a cough
and chest congestion, its likely due to involvement of the respiratory tract
or associated Gastro-Esophageal reflux.
Have her examined by a doctor and get her treated according to the cause.
Hope my answer helps you.