get a friend fat

My best friend who is in my grade and my age and has always been slimmer than me, and often rubs it in my face. I want to get fat, but have her get fat too so I dont feel as bad. Does anybody know of a pill or something that I could put in her drink to make her get fat? is there anything I could do to make her get fat without her knowing, because I know she does not want to. THanks!!!