Purrley,
I don't think that is cruel. It would be more cruel to have her loose in the house and getting hurt. As long as the crate is big enough for her to move around in.
Does she go potty during the day? Does she have plenty of food and water? I always leave a radio when I have to confine my pups. If you have food and water and she needs to go potty during this time, make sure she has papers or something that is not close to her food. You don't want her to get into the habit of thinking it is okay to poop where you eat.
So you live in Utah, we have a daughter in Richfield. I hear it is really cold there. It was 83 again today.
Take care and don't worry.