Do you have a picture? There are several websites you could post on, on their behalf:
I'm sure there are others. Have they contacted local shelters, to see if anyone is missing her? Even if it was a few months ago, they would probably still have the records.
Is there a reason why they can't have her inside? Maybe they could call some rescue groups in the area, to see if there is help available (a foster home). Failing that, kitty will need a shelter for the winter, under a porch or in an outbuilding.
Thanks for helping this poor cat out.