Why don't I like being Copied ?

I know I haven't invented anything but everything I do my little sister copies me. I decided to stop eating a lot a food to loose weight and next thing you know my sis is doing it. I put my hair in a pony tail then she does it. I don't like this feeling. Also when she copies she'll act like she done it better. She does it sneakily so I want see her copying me. How do I be more secretive??