I have had an unsprayed female mate with a male before and go through a false pregnancy. The male was not neutered at the time, but he was soon neutered after that. I also have had a spayed female before that was always nest building. I think the chances of your female being pregnant are pretty small. If you were planning on getting your female spayed, you could take her in right away. If you have a good vet that did the neuter, my guess is that your girl is not pregnant. Since she is not spayed, she still goes through her cycle, and is at risk for cancer.