I have a 2 year old QH filly that needs a feeding program?

I recently purchased a 2 year old QH filly out of cutting lines (i plan to make her a cutter) and i need to figure out a good feed for her. Currently shes on LMF Development (3 quarts) at night and 2 quarts of alfalfa pellets with equerrys probiotic vitamins. Shes not keeping weight on like i want her to, and shes already pretty small so i want her to grow. Unfortunately the hay i was able to get was the end of the year crappy cutting, so shes probably not getting much from that. any thoughts?