The best thing for her to rest in a dim and quiet room, and keep her warm. Chlorhexidene or a similar disinfectant can be used to clean her wounds twice a day. You all have some different wound creams in the UK. If she was squeezed, she could have internal injuries, but time will tell. If you have low dose 81mg aspirin, you can give her half of one 1-2 times daily for just 2-3 days. Secure your other chickens because it is time for foxes to be having young ones to feed. Let us know how she is doing. Pictures of her and the wound are welcome.