It looks like drainage from her nostril, probably from a respiratory infection. Those can be from viruses, bacteria, or even fungus. Since her comb color is not great, I would try to get her on some antibiotics in case of a bacterial infection. Tylan 50 injectable given orally, Tylosin powder, or oxytetracycline (LA 200) given as an injection may be used. The first and last may be found at feed stores with syringes and needles, while the middle one is found online at some pigeon stores.Those will treat mycoplasma (MG.) Make sure that she is warm, and in a place with good ventilation. Chickens with respiratory diseases need extra warmth while sick.