Actually- 40 degrees is not that cold LOL LOL for cats. Especially since she will be stressed and overheated from being that way. You don't want her to get too warm . I think the garage is a perfect idea and place for her to recover. This is what I do for the female feral spays. I bring a small carrier to the vet along with the cat in the trap. When they are done with surgery - they put the cat inside the carrier so when the cat wakes up she is inside the carrier. When I get home I have a large dog crate all set up and place the carrier inside of the dog crate. I take the door off of the carrier and the cat is still so out of it and is just too scared to move anyway. Then I close the dog crate door and leave her be for the night other than putting food in after about five hours. They usually let you feed/water and clean the litter box over the next twenty four hours. I usually release them after a couple of days. IF they are extremely stressed the day after the spay, I might release them early. But it is best to keep them for a two nights and then release in the morning hours. Good luck, Gloria AND even if a kitten goes in the trap with her - so be it. Then you can get that kitten done too at the same time.