If you have the Grow N Win, you could up that a bit. Then get some Buckeye Ultimate Finish and feed 1-2 cups a day of that for good fats. That helps with weight and makes them SHINE but doesn't make them hyper.
Does this horse hold her own out with the other horses? Does she get her fair share of the hay? There are 6 equine (4 horses, a pony and a donkey) where I board and my friend puts the hay out into at least 10 piles and usually 20-30 piles so that the horses can all eat in peace and not fight over just a few piles.
Beet pulp is good--crumbles are great if you can get them. I would not increase the grain though.