Hi Sonya,
Once the temperature gets above 40C or a bit lower if it's humid, chickens have significantly more trouble keeping themselves cool. A breeze helps which we've had confirmed recently here.
If you have air conditioning in the house you can bring two girls inside in dog crates or similar to keep them cool in the worst part of the day.
There are some good tips for dealing with heat in this topic:
viewtopic.php?f=8&t=8026784rand another great topic here:
viewtopic.php?f=8&t=7968802Some things that have been mentioned on this forum:
Frozen bottles of water in the pen
Frozen bottles of water in the water
Let the chickens out to free range and find a shady spot
Restrict heavy feed intake in the mornings on days when you know the temperature is going to be high - give more feed later when it's cooler
Shelter the coop or roof in some way - eg shadecloth to keep direct sun off the coop roof and give a bit of insulation
Keep water in drinkers cool and out of the sun
Some people will split a watermelon and put it in the coop for extra fluid and they certainly enjoy it
If there is a breeze, hosing down the coop or ground may help cool the area
Provide a paddle pool (eg kiddy shell) with water in it that the chickens can stand in
The things you can try will depend on your own yard and coop. We have too many chickens to bring them all inside, or even to let them all out, so we have to use a combination of strategies. Sometimes you can't do as much as you would like. The recent 46 degree days were always going to produce casualties. I hope you don't get that down in Victoria.
There's some information about heat stress in chickens here as well:
viewtopic.php?f=5&t=8019088I will borrow the pictures from there to show you what a heat stressed chicken looks like. They stand with wings out and will pant. Once they are prostrate on the ground they are in heat stroke and in serious trouble.

