Inge,

A friend, who lives in the country feeds "Bernie."  He doesn't know Bernie's sex, let alone if s/he has been spayed or neutered.  Bernie is gone for weeks on end, and then returns.  This happens even during the winter.  He eats, sleeps either inside (a room readily accessible to an outside door) and then goes on his or her merry way.  My friend is able to pet him, but he's still pretty feral. 

In the sixties when I was living in a lower apartment and had a cat door, I could not keep my two kitties who had been outside/stray cats in small quarters, so the cat door served them well (I'd lock it at night when they were inside).  "Nucat" would disappear for days, not particularly concerned about my anxiety, and would turn up dry (even if it had been raining) and smelling of having been inside someone's home.  Happy and had been well fed in his absence. 

I know Sarah is feral, but there is a good possibility she latched onto a person who had good food and good shelter. And indeed, she might very well return.  I certainly hope that this is the case.

You are so kind, and I know your heart is grieving.

                                                                      Bill