She's had a full vet check and her teeth are just fine. There are no problems with her lungs. She's just s...l....o....w and has always been slow. She's gracefully transitioning into old age, as I hope to do one day using her example, and there's nothing for her to get aggitated or angry about. My husband has a great idea for dealing with her situation, and we're going to construct it this weekend. We have a 50 gallon Rubbermaid trough that leaks, so it's not in use. He's going to pour cement into the bottom of it to weight it down (tips easily at the hands of our geldings), and then cover one half of the trough with a "lid" so only one horse's head can get in there. She can slowly munch away with no one being able to horn in on her muzzle. The others will have hay for distraction, and I think they eventually will get frustrated enough to give up. It's not that they can make her walk away from food - it's just that she'll share with them if they get their heads in there. I think this is a safe, inexpensive idea that surely worth a shot. I'll let everyone know how we do!