My 3 year old daughter is abusive to my 1 year old daughter.She scratches her and she hurts her and makes her cry.What can I do to stop this behavior?

Every single time she hurts her you NEED to put her in a time out. She should not be able to get out unless she hugs andsays she is sorry. Nothing will work unless you are consistent and do it every time. Finally she will stop. This happen very often. Make sure she is getting the attention she needs when you aren't holding the baby. She needs your attention. She loves you and she needs to know that your love hasn't changed even if she has a stinky little sister. Wish you well with this.