That looks like a serious case of bumblefoot, which is a staph infection that can kill a chicken if the infection is untreated. There are several links and videos on YouTube that will take you step-by-step through the process of treatment. Or, if a vet is an option, I would advise you to make a visit. Best of luck and lots of bear hugs as you treat your beloved chicken!
There is nothing on the bottom of the foot... I’ve soaked several times today in Epsom salt and been managing to wiggle the dry hard thing out. It’s half off but I’m scared I’m hurting her and it’s bleeding a bit. Does the abcesss ever get full and drain itself?