Am I the only one who doesn't think she looks skinny? Maybe needs a tad more weight but I don't think she looks that bad. Needs muscle and I think it's very obvious she's still growing and that her body will change and also bulk up a lot in the next few years. I wouldn't stress to much about her condition. Just keep on pouring groceries in. Do you ride her a lot? This isn't a horse I would suggest starting young, but sounds like it's already been done. Just go slow and give her plenty of growing time.