A few months ago we took a stray cat that showed up at our house to the vet to get her fixed so she can't get pregnant. Now that it is mating season male cats outside will not leave her alone. They bite her neck and try to mate with her. Is this normal? If so, why are they doing this since she cannot get pregnant?

Yes it is normal. Once an animal has been through it there is a pattern established and it takes a few seasons before it changes. That's why in most cases it is recommended to have the animal fixed before ever going into heat.

The thing is she was fixed before she went into heat and before she ever got pregnant. She got fixed before being full grown. She had never been in heat before.

Will a tom cat mate with a pregnant female cat

Will a tom cat try to mate with a pregnant female cat