Ouch.. That looks pretty painful. I'd soak the foot in something against infections.. Warm water and epsom salt? You want get rid of all dry blood, debris and such so you have free access to the wound/infection so you can treat it. After the soak, I'd put some antibiotic ointment or similar on the foot. If she's not walking anyway, I might even try to cover the foot in vet wrap to keep dirt out and keep the ointment in and then I'd repeat the treatment every 12 hours or so.
Keep her on her own while she's not walking. The wound could be caused by a cage mate pecking her toe.