The first cause for aggressive behavior in young children is simply temperament. In other words, some children have a more difficult time than others learning socially acceptable norms about displaying emotions and interacting with others. These children benefit from a clear consistent parenting style that includes limit setting and a system of rewards and punishments for good and bad behavior.
If, however, you feel your child's aggressive behavior is more than simply temperament, then there are a few other possibilities to consider.
The first is attention deficit disorder. Children with this disorder often have problems with impulse control, and this can manifest as aggression in their social interactions. This diagnosis would be more likely if your daughter also has other typical symptoms, such as hyperactivity or inattention (for example, if you feel she never hears what you say because she is too distracted to listen).
A second possibility would be an autism
spectrum disorder. Children with this disorder sometimes have aggressive tendencies, especially when their boundaries are invaded. They may also exhibit odd or repetitive behaviors and tend to be socially withdrawn and have trouble interacting with their peers.
Regardless, it sounds like your best first step is to schedule a visit with your daughter's pediatrician
to discuss your concerns and to determine if further workup is needed.