The other thing I remember we introduced at about this time, which was/is a life saver, is 'More' and 'All Done' signs (sign language). For 'More' we just used fingers from one hand into the palm of the other, and for 'All Done' we used wiping hands together, like one would on a napkin or when you are washing your hands.
She picked these up very quickly and it soon helped us to understand when she was done, or didn't want something, or wanted more (without screaming, throwing food, spitting, etc.)