She could have gashes and punctures under her feathers that need medical attention. Go out after dark and grab her off her roost. Keep a firm hold on her legs with one hand and she will stop struggling. Yes chickens are resilient, but an infected wound from a preditor attack can be fatal, and should be treated ASAP. If you are going to have animals you need to be prepared and take charge when the situation arises to do what is necessary. Fox will take your chickens any time of year by the way. This fox sounds young and inexperienced. Most chickens do not get away. I hope she recovers.
We had a husky attack years ago. All of our chickens survived but one of them (our oldest) got bitten quite badly. I didn't notice any wounds until a day or so later when I found a large bite in her back. We treated her and she pulled through and lived a good life passing away last year at 12 and a half.