I feel like a failure as a mother? What can I do to help my 15 mo daughter?!?

Keep encouraging her. Although I am not a mom, I can well assure you that encouragement will help her. Talk to the pediatrician about what's going on. Props to you for even sacrificing a classroom environment to be with her. Not many moms care that much these days so I'm proud for you. Keep up what you're doing!!! You are so not a failure. The only people who fail are the ones who fail to try.