It could be she stepped or climbed on something sharp. Soak her foot/feet in warm Epson Salts and swish the water around for about 15-20 min. It looks like her feet and legs are not only dry but dirty. Use any gentle soap like Dawn soap for washing. Rub her feet and legs to clean the scales on her feet and legs. You can use a soft bristle toothbrush. This might take longer than 20 minutes then dry. Then message a liberal amount of Vaseline onto her toes, feet and legs. Apply a Triple antibiotic on the little sore/abrasion area. You may have to wrap this particular area to keep it clean during the day. If you do this before roosting time, the Vaseline/Triple antibiotic can better stay on her clean skin all night. Repeat this for several evenings until you notice an improvement difference. This will also allow for some good bonding time with her. Anytime a chicken has any type of injury, they are stressed. Cooking her a scramble egg will boost her protein and the sore will heal quicker. The key will be to soak nightly, message Vaseline and apply a liberal amount of the Triple antibiotic oint. Then set her on her roost. This may sound over kill but, your chickens foot will heal up. Check out the coop and run to clear anything that she may have stepped on to injure her foot. I am glad you noticed this sooner than later as you are ahead of the game to healing up her foot.