My "bestfriend" has been really getting on my nerves, and now she's taking it too far?

Tell her how u feel! She shouldn't be doing this! If she's a real friend to you shell understand that you mean what your saying and see it's bothering you. But if not she's not a good friend. But whatever you do, never give her a taste of her own Meds because it's only gonna make it worse. Take to her calmly and if it doesn't work, take to a parent or Teacher.