It looks like possible bumblefoot, and it is on the other footpad more mildly. Damp or soiled bedding, rough roosts, even the poop itself, can lead to footpad dermatitis or bumblefoot. If ventilation in the coop is not good, dampness may not dry out. Are there any sharp rocks where she is kept? Are you using a gamebird type feed? I agree that soaking in warm Epsom salts water or a little Betadine in soapy water could help if done over several days. Some people use a dressing on the feet with a little sugar mixed in Betadine made into a paste, and change it every other day. Here is a good article to read:
https://www.farmhealthonline.com/disease-management/poultry-diseases/footpad-dermatitis/o