I would go back to basics with this one. Turning her bum to you is very disrespectful. It could potentially get quite dangerous if it develops and she could eventually kick.someone in the head who happens to put a feed or water bucket down at the wrong moment.
I would tackle this outside of the stable with ground work. Do a little every day. Teach her to step aside, manoeuvre her quarters out of the way while her head faces you. All the basic patterns. She should eventually be able to do this with a loose rope and minimal, light touches.
Personally, I rarely use treats, especially with a greedy horse as it can encourage the barginess.
Obviously you have to get her out of the stable to to do the training 
, so I would get some help with that from an expert, don't struggle on your own. I would take the opportunity to give her a health check too. See if she has any stiffness in her neck, or has hurt her poll. Obviously a headcollar shouldn't be hurting her teeth but she may associate it with being ridden, so you could get her teeth checked too. Just check basically that the defensive behaviour is definitely associated with food and she is not protecting herself from pain.
Another idea: maybe you could get her tied up elsewhere without a hay net and once she can stand politely, with a slow feed hay net. Extend the period of times she does this? Then transfer that behaviour to the stable? Then loose in the stable?
This may take a bit of patience and time to get right. And if you are able to do this, I would vary the time and manner in which she is fed (as long as she doesn't go too long without obviously) and mix up the routine a bit so she doesn't get in to too much of a froth around feed time. Also, add more interest to her day where possible. Good luck.