Thought I'd step in with some chicken anatomy info after I cracked open my old animal anatomy books from college.
Chickens (and all birds) do not have the muscles in their ribs or a diaphragm under their lungs like mammals do. Additionally, their lungs don't expand and contract quite like ours do. To breathe, they actually expand and contract their lower abdominal walls. The 'contracting' you see might actually be her breathing

The air is drawn in when they relax their abdominal muscles, enters through their nostrils and beaks, goes down the trachea, through their major lungs, then into the air sacs located around her body. Then they contract their abdominal muscles and the air sacs empty through the lungs, and back through the trachea, and out through their beaks and nostrils. They actually scrub the air of oxygen twice for each breath they take! It's a pretty unique and interesting way of breathing.
The vent gleet, on the other hand, can be irritating to the bird, and can in very extreme cases scar their vent and make it hard for them to lay properly. If you have a warm place to put her for a while, take her in, wash her 'butt', and let her dry, then apply some human anti yeast medicine to the area (wear gloves, of course). You may have to treat her several times if it's really persistent. I have a hen that's driving me up the wall with it too, but she's one of my best and healthiest birds otherwise. Adding some yoghurt to their diet every other day has certainly seemed to reduce the 'nasty bum' symptoms.