I am having this issue as well, right now. All you can do is get as much of it out as possible, pack it with the antibiotics your using and keep on rapping and doing an epson salt soak. This will hopefully draw out the infection to the point where you can easily get it out.
Triple antibiotic cream is best and is per-scripted by most vets. If you wrap her well with vet - wrap she should be okay to go in with your other chickens. Just make sure her environment is extra clean. Be sure to check your other chickens for bumble foot, if you haven't already. For prevention...