Can spayed cats (female) go out at night for mating?

She definitely isn't mating, letting a spayed cat out can lead to some severe injuries though. She's not actually going into heat, she doesn't produce those hormones anymore as she had a full historectomy when she was spayed- no more female organs at all. It's time to put out flyers, you aren't going to be able to ease your mind until you at least find out what happened to her. Good luck!