Oh dear, im so sorry to hear what you are going through. Have you contacted Family Assistance or even the Salvos to see if they can help at all? I know its probably not enough but may help a little.
You are not a failure at all. You are providing your little girl with all the love in the world. If anything you are helping her get through her day to day life.. you are being a wonderful mummy to her, she wouldnt be able to do it without you. Things will get better.. you just need to get over this little hurdle in your life and youll find the light at the end of the tunnel.

Big and i for you things will pick up soon.