My first thought would be Mycoplasma Synoviae. It primarily manifests as hot, swollen legs and joints which later blister. This would account for the scabs on her legs and comb - basically the blisters healing. Tylan soluble is the preferred treatment but only seems effective in younger birds at the acute stage of the disease i.e. if given when the symptoms first show. So probably too late to treat her with this. The enrofolaxin should work but if it is m.synoviae, it's unlikely to completely clear - whatever you treat with - as it becomes too entrenched in the air sacs and hollow bones. Blossom will be a carrier for life and could infect other birds in your flock. I'd continue with what you're using and give good supportive care. A splash of cider vinegar in her water has been found to be useful too.
Denagard has had good results as a treatment but should not be given to birds being treated with coccidiosats as it is toxic combined with these.
Is it possible your soil has a heavy burden of e.coli? E.coli is often a factor in reducing immunity in birds and allowing other diseases in. E.coli thrives in poorly drained environments. Just thinking about your old death coop here.