The best way would be to try and put a collar on her with a message, in case she has an owner somewhere who doesnt realiese her cat is abit of a floozy!!
This happened to my friend. Fluffy just walked right in stayed around to have 2 litters of kittens. My friend rehomed all except Harvey and Grace, who lives with me and is currently sitting on my mousepad! Then after neutering she decided to live outside all summer just coming in for food.
She is now coming in more with the bad weather.

Maybe you have been chosen by a free spirit! Good luck with her..