STOP SWEET FEED, and oats! It's counter-productive for "hard keepers" and horses that may have ulcers. And definitely not good for horses with eating/chewing problems.
Get her on a diet of alfalfa pellets (2-3 scoops, 3qt feed scoops), stabilized rice bran (1-2 lbs), Source Focus WT, and NutriPlus++
. No other feeds or supplements. This is a balanced, complete diet when fed with grass or timothy hay.
Or, instead of the Focus and NutriPluss, you can put her on Platinum Performance
Find a good equine dentist (who is ALSO a vet!) and get her mouth really looked at. She could gave equine equivalent of TMJ or some other jaw/mouth problem that is causing her teeth to wear unevenly. Make sure her wolf teeth are removed if she has any (not just filed down).
If she does and it cannot be fixed, then you'll need to replace her hay with soaked hay cubes. The cubes will provide the long-stem fiber she needs and are easier to chew.