Did you measure her temperature at that time? Were the surroundings hot?
It may be heat exhaustion
This happens when kids play in hot environment which is not well ventilated, also with poor fluid intake.
Kids due to various reasons are prone to get heat injuries.
Make sure she wears loose and comfortable clothes and drinks lot of water/ fluids with electrolyte and sugar.
Since you say it has happened several times, its better that you discuss about this with your pediatrician
And what was the BP and blood sugar last night?