Back-Talking

How is it that Kenzie ,who is only 14 months old and has a vocabulary that consits of ma-ma, da-da, pa, kitty, doggie and tiki, can back talk me? Her usual lunch is made up of peanut butter sandwhich, gold fish, and some kind of fruit...this is her favorite and because she is so picky I don't ever change it up. She likes her tray clean at lunch time (not literally) Today I figured I would try to change it up and give her some left overs from last nights dinner because she loved it so much. I warmed it up cut it up and then gave it to her thinking she would be thrilled! WRONG all I got was a baby throwing food at me and when I sternly told her NO she started to back talk! I could not believe it...it was so hard not to laugh but she needs to learn that is not ok! I just can't believe at 14 months old I already have a mini me! What am I gonna do? :)