N.M.
Hi! I'm not sure if you are looking for a high calorie type powder or not, but our DS who is now 2 years old is on Carnation Breakfast powder drinks.
We give him soy milk and like your DD he LOVES his milk. He is only in the 4th percentile for weight which is why his doctor has him on the extra nutrition/calories. He was on Pediasure, but she said we could switch to the Carnation Breakfast powders since it is cheaper if we wanted and has the same effect.
Oh, and you can buy them at any grocery store in the breakfast/cereal aisle.
HTH!