Could you post another picture of two of her head in a normal position? Several things can cause swelling of the face and wattles, including tick bites or insect stings, and certain diseases such as fowl cholera and coryza. I suppose a snake bite might do that, but I would think the chicken would have more swelling around the neck and be having breathing problems. If she is alert, eating and drinking, and acting normally, I would just watch it. You could also give her 1/2 of a children's Benadryl orally, or crushed into some egg or yogurt. Just do that once, and see if the swelling has gone done some by tomorrow. Let us know how she is doing.