spay??

I would get her spayed if I were you. Especially if you usually let her out. Once she goes into heat again, the boy cats will find her, no matter what floor you live on. Plus, it will keep her from crying and trying to get out when she is in heat. I don't know if you have anything like the ASPCA or Humane Society where you live, but here they can give low-cost operations or vouchers to use at the vets office. Everyone I know who owns a cat has had it fixed, and none of them have had problems with it; and the cats are also much happier and easier to live with. Good Luck.