It might be fowl pox. Or it may just be from other chickens pecking her.
There’s no cure for fowl pox, but there are ways to treat the disease and keep your birds comfortable while the infection continues. You can also give the uninfected birds in your small backyard poultry flocks the fowl pox vaccine for fowl pox prevention.
Furthermore, once a chicken has survived fowl pox, they develop an immunity to the infection. Vaccinated birds have a higher chance of not being affected by it.
If fowl pox enters your flock, isolate the infected birds. Contact your veterinarian to see if any antibiotics can control any secondary infections that result from the disease.
You can keep an infected bird comfortable by keeping the coop clean and eliminating stressors in their daily activities. You might also use antiseptic, ointment, or other veterinarian-approved products to clean and soothe your birds’ scabs throughout the infection.