As a caretaker to feral colonies, I agree with barncat. Some you can socialize and others you can't. But.......and the most important things always come after but..........you are providing her with all the things every cat deserves, food, shelter, warmth and love and those are the things that really count. She does trust you enough to allow you to rub her ears and that is a big step. Just hang in there and keep tyring but accept with she is willing to give you back.