Unbalanced can mean multiple things. It depends on the context of the conversation and with whom. If it was a farrier for example, it would be her hooves. Chiro - could be out of alignment. Trainer or another rider - could be her way of going under saddle. Judge in halter class - her build & angles. Etc.
Need more info to help determine what is meant. Pics & video would be a great help!
Life is like a camera. Focus on what's important, Capture the good times, Develop from the negatives and if things don't work out, Take another shot.