Looking at the picture you provided of her foot, it looks like you could give her a good 20-30 minutes soak in warm water (hot but not uncomfortable on the inside of your wrist if you dunk your hand into the tub of water) preferably with epsom salt as she'd benefit from the salts, but not mandatory. After her spa treatment, rub her feet with a dry terry washcloth or towel, from the legs down, and from her 'heel' to her toes (don't rub against the grain of her scales). You're hoping that the scabby part of that bumble foot will simply pop off, or at least get a loose edge on it to give it a good tug off of her foot, opening the wound, so you can squeeze the pus out of it. Chicken pus is not liquid like human pus, it's more like cheese in consistency. If you're not successful in getting it to open the first time you soak her, you can always give her another spa day the next day... and if it simply doesn't seem that you'll get the wound open this way, you may elect to either take her to a veterinarian to have them lance it, or you can watch some youtube videos on the subject and perform the minor surgery yourself. Only you know which option is best for you and your hen. Assuming that you've managed to squeeze the pus out of the wound, give it a final rinse with water to determine if you got ALL of the pus, if not, it will simply fester again. Once convinced that the infection is out of the wound, pack the wound with triple antibiotic ointment without pain relief (neosporin type of medicine, consistency of vaseline), and make her a little bootie with some sports tape in any color but red (the kind that sticks great to itself, but doesn't stick to your skin). Remove the bootie in a couple days to see if the wound appears to be healing properly. If not, back to soak, open and drain. If so, remove bootie and visually inspect the wound periodically.