Do dogs get grumpy in the heat too? gsd acting up today ?

My gsd is about a year old well trained and usually well behaved. Today was a HOT day in MI and we were all miserable but she seems to be too. Shes been snarling curling her lip and snapping agitated ears back and under foot non stop today. We keep having to make her go to her kennel to relax and for safety because she snapped and growled at my 7yr old when my gsd was getting impatient as i was about to let her outside. We have been having probs with her curling her lip at my 7yr old as well ever since we got her but normally not this bad. We adopted her at 6months. She is utd on everything and is hydrated so whats her prob?