Foster failure

No, this is not the usual kind of "foster fail". This is a sad story. Today I had to take my foster kitty, Sarai, back to the shelter. I've had her for 6 weeks and really have made no progress. She would come up to me for pets and even roll over to be petted (and let me know when enough is enough) but I have never been able to pick her up. The one time I even got close she tore me up. So finally the decision was made to trap her and take her back. I felt absolutely awful, like I had betrayed her, but honestly, I'd tried really hard and tried everything I knew, but she'd never gotten any closer. The foster coordinator was honest with me, saying that they'd do another behavioral assessment but might be moving forward with euthanasia since she isn't eligible for the barn cat program (she's never lived outside) and doesn't seem adoptable at this point. I feel awful.