Well it's going to be hard to sit and watch her being it's winter. So it will have to be elimination check inside their run and coop if there looks like any possibility she might be sticking her bill under something. It's amazing where they can stick those bills. Try using some antibiotic...
Could she be sticking her bill under fencing or something else that might be causing problems?
I just don't think she would have fowlpox in winter unless your in the south where mosquitos are still abundant.