Thanks for placing your query here.
I can appreciate your concerns.
First of all there is no need to panic.
Following additional info would be useful to narrow down diagnostic possibilities.
*Any heart related concern in past ?
*Was any heart murmur
noted at any routine checks?
*What is her sleeping heart rate
*Current medications ?
can be due to many cough syrups,fever
itself or primary heart problem .
is very poor in detecting heart problems.
EKG changes might also not be very sensitive or specific.
Please consult a pediatric cardiologist & get an ECHO done.
This will certainly settle the matter for good.
Hope I have answered your query.
If you have any further questions I will be happy to help.
Wish her a good health.