What to to do if someone is slandering my name?

You can sue her for defamation. Defamation is the public (so to any other people, including purely orally) making of untrue statements of fact (so opinions are not defamation; but saying you did something which you did not is an untrue statement of fact, for example), which damages a person's reputation. If you have been slandered, you may be entitled to monetary compensation for it (which can also provide vindication). Since at least some of the things you write that she has said are factual allegations which could damage your reputation, it would seem to be worth it to speak with a personal injury attorney about this matter, so you can evaluate the strength of the case and its worth (and cost to pursue). Also, if there is some school behavior/honor/etc. code and this student is breaking it, you might report her to the administration--maybe she can be suspended or otherwise disciplined.