I can't add much to what was said, but definitely watch for "missing cat" signs and ads as well. Are there neighbourhood stores with public bulletin boards? They are a great place to look for these ads, and also to put up found notices. As for the big shelter - do they have a lost and found section?

Thank you for feeding her - poor girl! She could starve before her family is found, if they ever are.

Just to screen for the actual people that say they own the cat, have them tell you the colour of collar she is wearing. And how she went missing, if you feel suspicious.

Not to be paranoid - just sayin'!

I remember you, though! Isn't there a feral family that lives in a small shelter your family built in your back yard?