Cat in heat?

I've been supporting a cat that was abandoned when a neighbor moved. She lives outside but comes in through the cat door to feed in the house.

For a few weeks she wandered around my back yard mewing but not really meowing like a female in heat. Is it possible she was in heat and different cats make different noises? Or maybe she is young and hasn't learned how to really holler at a man? 'Cause if she isn't altered, I need to remedy that pronto.

Thx.