How will a VERY misbehaved 8 year old effect my 4 year olds attituded and behavior?

the 8 year old has temper tantrums (4or 5 a day), screams, hits floors and walls, She hits, kicks, pushes, Talks back. Purposly doesn't do what is asked of her, She ignores you, She repeats stories and questions (even after you answer her) She cries over everything she follows you from room to room, she NEVER plays. unless its to play Mommy and Son so she can boss him around. She also is VERY Mean and makes Mean comments all the time.