Chicken having trouble opening its beak

[Henhorse123]

My chicken is getting over the shock of being attacked by a dog. It has been about a week since she was attacked and only just started drinking properly yesterday. She has eaten very little, but we put her outside with her friends and she seemed to perk up, she showed an interest in the food but when she pecked it she didn't open her beak. Is this just bruising or has some thing bad happened to it? I have had them for about 2 months I don't want another to die.