Come up with some consequences for her behavior. If talking and time-outs aren't working, try taking away priveledges. Things such as TV, video games, computer time, CD player, certain toys, and playing with friends seem to have worked for me. Be sure to talk to her when the behavior hasn't occurred about these new consequences. For this to work you have to follow through. If her consequence for hurting the 3 mo. old is having her Barbies taken away for two days, don't give in to any crying, whining, pleading or promises never to do it again. You must also give the punishment right away. Don't threaten to take priveledges away, just do it. Her behavior sounds out of control. How does the father handle her violence toward the baby? Hopefully you can talk about it and form a plan youand he both can work together on. It definitely sounds like the child needs boundaries. Until boundaries are set for her, her bad behavior will continue/worsen. Remember that children thrive and feel safe when they have boundaries. When they are allowed to do whatever they want they feel out of control and will behave like that. Don't let this girl run the show with you. Let her know in a calm voice that you will not tollerate her behavior anymore. Then tell her what will happen if she hurts your baby again. Be calm, be serious, be loving. Explain that you would do whatever it took to stop someone from hurting her and you have to do the same for your baby. I hope you can work through this. Good Luck.