It would be a very good idea to snatch her up and get her to a vet to be spayed, otherwise you're going to have a backyard full of tomcats spraying everywhere, howling, caterwauling, fighting. Then you're going to have a backyard full of kittens . . . and there will be that many more unwanted babies out there in the harsh world. Cats increase exponentially.
If she's already been spayed, she might be crying because she's lonesome. Contrary to what many people think, cats can be very affectionate creatures and can crave companionship. They're also adept at choosing their people. If a cat chooses you, consider it a high compliment. They're generally much more discriminating than dogs, lol!