We're so glad you took the time to reach out for some help and guidance with your question. Nobody deserves to get treated poorly, so hearing that a girl is taking things way to far by being mean to you really shows just how mean she is being. You don't deserve to be treated that way and its really awesome to see that you are reaching out for some help on how to handle this situation, rather than allowing your emotions to get the better of you. The last thing you want to do is lash out at this girl because that can just escalate things or get you into trouble.
Depending on where this is happening, it is always best to reach out to somebody, like a teacher at school or a supervisor at work. Get some eyes on the situation to get it under control. It can be really tempting to try and handle things on your own but, again, that usually just backfires and makes things worse. Opening up to somebody with authority can really do a lot to get things under control. Also, most schools have some type of anti-bullying policy so if this is happening at school talk with the school counselor or a teacher and ask to go over the anti-bullying policy. Then, figure out what they should be doing to help get this under control. You definitely don't deserve to be treated this way.