I'm thinking of ghosting a girl in high school
Why do you think you need to ghost her?
No matter what I say she always has a comeback for it
You may feel frustrated in your communications with this girl, but cutting her off without explaining yourself is not how to handle things. Speak with her about your issues and work it out instead.
I always have the perfect comeback for everything she says
I understand, but it feels as if your banter with her always involves comebacks so it may feel very weird for you to ghost her if you both enjoy having friendly comebacks with each other. If comebacks are not okay for you, then you should communicate with her and tell her that you should stop the practice, instead of not saying anything.