Hey. You has asked me about what I fed my my skinny TB to make her gain weight. She got 1 flake in the morning, grass all day, and a whole bale of second cut hay at night. For grain, she got 1gallon, the soaked, beet oulp shreds 3X per day; Alfalfa pellets (i don't remember how much) 3X per day; and 1/2pound MVP, 3X per day.
One thing to keep in mind, with all of this food, your horse will become a little "crazy". She will need yturnout everyday and, ideally, riding or excercise. On days she does not get excersize besides turnout, cut back her a grain a bit.