Agreed. Sweet feed, ick. First, have a vet check her teeth, second, have a fecal egg check done on her poo by a vet for any worms. Then get her on a high fiber and fat diet, NOT a high sugar diet, such as sweet feed. Sweet feed gains weight with sugar, while it does its job, you need to feed a lot of it to make a difference and then you have a over reactive energetic horse on your hands, not to mention the unhealthiness of it.
I would recommend lots of beet pulp and rice bran, beet pulp has lots of fiber and rice bran has fat.
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown