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It could be the early stages of bumblefoot or infection of the foot. It does look irritated.
Inspect the little dot that I have circled, she may have poked her foot on something.
If possible, get someone to hold her and get more photos that are clear, I know it's almost impossible to hold one yourself and snap photos, just when you think they are holding still, nope.
I'd try giving the foot a soak in a warm epsom salts bath. Dry the foot, then apply a dot of triple antibiotic ointment to the foot pad. Apply a tiny square of nonstick pad, then wrap the foot. Coban/Vetwrap/Sportswrap works very well for wrapping. Check the foot daily and repeat the soaking/ointment/wrap. See if the swelling goes down and the foot improves over a few days. If it gets worse, swells, has an odor, etc. then stop the treatment.
If she's in a coop/run that stays relatively dry, then I'd let her with her flock, keeping the foot wrapped.