C.M.
brush your teeth when she is brushing her's. Tell her to spit out the "bubbles" like mommy does. That might help. When my middle child was learning to brush his teeth on his own, he always did what his older sister did. So I had her brush her teeth the same time my son did. he thought it was fun to spit the bubbles out. It seemed to work. Sometimes he forgets still to this day, but about half the time he remembers on his own, or I have to remind him of spitting out the bubbles like sissy does. Good luck!