she have been light headed from the heat or she had a slight case of heat stroke 9 not TO serious ). just take her to docter if it continues , and always remember those " time to come inside breaks " to get water and re apply sunscreen. Also make sure she has lots of water even i know some little kids dont like it.
hope i helped
Maybe she has fractured it when she fell if it hurts and she cant move it take her to the Doctor or ER to see if there is an injury..it sounds like she may also have heat stroke , so def get her looked at ..Best not to have her play out all day ,at 4 year old it is too much, , she also needs plenty of water and light clothing, a hat and glasses.sunscreen ..