Children love attention and they will do anything to get it. If the only way to get your attention is to do something bad, it's not hard to figure out which behavior she'll do repeatedly.
Try to catch your child doing something good. Call your child by name when you see her doing something positive. You might say, "Kelsey, I saw you help your brother put on his jacket. That's great!" After she gets over the initial shock of hearing her name followed by something positive rather than negative, she'll smile proudly, stand a little taller and make an effort to get caught doing something right in the future.
Stay away from generic praise such as, "You were good today." Find specific incidents which define good behavior. "Thank you for remembering to pick up your toys," and "You took turns with your sister," describe the behaviors you want from your child.
Praise and attention are powerful motivators. Catch your child doing something good this week and comment on it. Your child will love the attention and you will have added something new to your bag of parenting tricks.