Help! My Little Sister Has To Go To Court! What Do I Do?

okay so theres this girl in my little sisters class, who is legitly fat,, she is 250 and in the 7th grade and she called me sister a fat trashy hoe and my sister came home crying so me and my brother were looking for here and when we found her she called me a stupid skank and my brother a walking std and none of us are any of those, so i asked what she said and she said i called u a stupid skank and shooved me, so i hit her and my brother said if she tells any one this she will be hit harder and this time by my little sister, and instead she goes to her dad who is a cop and says that my sister harrased her and **** and now my sister has tio go to court. what do i do?