My kitten is being TOO playful is agresive. How can i make my kitten be the nice loving kitty i had before?

I bought 2 orphaned kittens a boy and a girl. Mr. whiskers and lila. Whiskers is fine. He does his own thing, but Lila doesnt. She has begun beign agreesive toward me and whiskers. She used to love whiskers now she being to rough.I tried everything in the book... Ive even had her isolated in her age. she only come out to go to her litter box. plz..help