Even though at 11 months she may understand what you're saying or what you mean, her brain is not developed enough for her to emotionally cope with the dissapointment of not being able to do/get what she wants. Babies need help to develop correct emotional pathways. The book "what every parent needs to know" explains all of this really well and i highly recommend it.
It helped me to see my baby was not trying to be controlling or manipulative, she was just too little to handle her emotions and needed some help.