from an Aussie dog breeder here.
Blue Healers or Australian Cattle dogs are bred to work all day herding cattle and driving them when the herd needs moving. Not unusual to do 30 miles without stopping. The heat really won't affect them - they can take 100 degree plus days in the Outback of Australia no worries.
If she gets hot or thirsty she will actually stop and take a drink / rest - in the postion you have in the photo - for a few minutes. Honestly you will be very very unlikely to tire her out from throwing a ball - she sees this as work and they absolutely love it.
You've got water out - that's all you need worry about. She drops the ball in it to cool it down and get rid of the saliva on it as well - they're bloody smart. Have fun and don't worry about the Cattle dog she'll know when to stop.
