I'm no chicken medic....but...
She may have tweaked it on something....sprain/strain.
Dark color could be bruise or necrosis, only time will tell.
Epsom salt soak couldn't hurt.
Looks like some raised scales,
could be the start of scaly leg mites,
might want to pack those with vaseline or bag balm or oil.
For limpers, this is what I do...
If limp is really bothering them by inhibiting their normal activities too much, I will isolate them in a crate to 'force' rest for a day or two. Letting them out late in day, an hour before roost time, to give them a stretch and evaluate their mobility, then decide if they need another day and put them back in crate off roost after dark. Repeat stretch and eval the next day until they are better. Keep crate in coop so bird can remain 'with' the flock.
I like to use a
fold-able wire dog crate (24"L x 18"W x 21"H) with smaller mesh(1x2) on bottom of crate under tray.
Then you can put tray
underneath crate to better observe droppings without it being stepped in. If smaller mesh is carefully installed, tray can still be used inside crate.
Can toss a chunk of 2x4 on crate floor for a 'roost' to give a break from feet being on wire.
That's all I got, the others tagged may have better diagnostic experience.