Bullying problem at school?

So I'm a sopre in high school, and in one of my cles there is this girl I have I have an igned seat with at the same Table as her. I'll call her "Lisa". Lisa is always on my case and always so rude to me. Like today we were doing this activity with our Table group that she's in and I wasn't sure what to do so I went and asked the teacher for help. After I was done talking with the teacher she yelled over to our Table and said "Guys Karleigh is lost will you please help her?". Then Lisa said "You don't get it? (in a really rude voice) then I could hear under her voice her calling me retarded. This isn't the only thing Lisa has done. I have tried ignoring it, but it's getting to a point where I am Truly getting hurt. Our teacher has this little mail box thing where we can write her letters about situations we have. I was thinking about doing that, and asking the teacher if I can be moved away from Lisa and for her not to tell Lisa I told her, because if she did, Lisa would be even more a ***** to me. But I don't want to sound like I'm tattling. So my question is should I just tell Lisa off, or tell the teacher? (If I did tell the teacher would it be tattling?) And if I wrote her a letter should I explain whats going on and why I want a new seat?