HELP - Hot summer weather

My 7 month Goldendoodle seems to get diearrha when it is exteremely hot outside (40c) .
She is in airconditioning for the most part - only outside for short walks & to go to the bathreoom.

I've had her checked at the vet & they say she is perfectly healthy.
Is this common in Doodles? & does anyone have any suggestions to help this....