HELP! Can 5yo hen be treated w/monostat for yeast infection?

My RIR seems to have a HEAVY yeast infection. She is prone to being crop bound, and 2 winters ago I nursed her back from death's door by feeding her veggie oil and water with an eye dropper and massaging her neck until her strength returned enough to be able to eat & drink on her own. I noticed her doing the neck "stretching" thing again (where it looks like she's choking), but I didn't feel any obstruction. She has much white cheesy discharge from the vent, she holds her rear in a drooping position, and walks funny. I thought I read that nystatin should be given (on this forum?) as well as raw apple cider vinegar (which we put in their water anyway). However, no vets in my area say they treat birds, and I don't know where to get nystatin. Should I feed her yogurt? Any other suggestions?? Thanks, Liz