Envy

Brooke has an overly close relationship with her older brother Brian, so much so that when their parents moved away, she refused to go with them and demanded to stay and live with Brian instead. Brian Recently got a girlfriend named Kat who hes been spending all his time with, but with an overly jealous little sister it begins to start problems... especially when she finds the both of them shrunken down to 1 inch tall...

Personally think this is my most favorite story yet!