Every horse is different. I own race bred barrel horses and for the more high strung I try to stay away from feeds with tons of sugar. Barrel horses are also prone to ulcers. Try to avoid grains that will cause issues. She is still a baby, so u also want to be careful not to overdue thw grain anyway so she doesn't grow too fast.
Ultium!!! I swear by it! My friends ottb looks like a quarter horse and she runs her in barrels!
Purina strategy is what I use. Triple crown feeds are also good