What attacked it? Do you know?
Gently clean the wound well with clean water and put a bit of Neosporin or other such ointment that is safe to use on birds.
This is the only advice that I have, unfortunately. I hope that someone else with more experience will be able to help you more.
Good luck with her.
My dog in the past would horribly attack my chickens. There were some I felt would not survive but they did. I think @Sapphire Sebright's suggestion was correct, all I can add is that we put our hurt chicks in a very dark comfy separate area until they recovered. Also be sure to give it electrolytes and Probotics during recovery. BTW: I can not tell ...is that the back of the bird that is injured?