You could also look for alfalfa cubes or pellets and try adding that instead of alfalfa hay, along with what you're already giving her. During the drought, that's the only way we could find alfalfa in any form. Its a bit expensive but ships and keeps well so there should be someone in your area that would have it.
Also,nixing the sweet feed and adding a specialized pony feed (we use Purina Miniature Horse and Pony and it works great) might help as well. Sweet feed really isnt nutritious and is probably adding to that hay belly.