It's very unprofessional of the teacher.
1) Go to the teacher before or after school, when there won't be a hallway full of people watching and when you won't need a hall pass. Flatly say, "I don't think it's fitting for a person in your position to gossip about me with other students." If saying it out loud is too difficult, write it down, hand the teacher the note, and ask that the teacher read it. You can walk away after you say it, or you can choose to stick around and have a conversation about it. It might help if you give particulars such as the student's name that she gossips with and examples of things they've said about you. This gives the teacher a chance to fix the problem on his/her own. It also gives them a heads-up that you're beginning to take actions. If/when you report the teacher or discuss the situation with someone else, you can rest assured that you gave him/her a fair and ethical chance.
2) The next step is to see a counselor at your school. Bullying is a hot topic these days, and the counselors have to do something about it. Just let the counselor know what's going on, including a bit of your history with the student. Don't sugarcoat anything.
3) If the counselor can't help enough or if things don't change, go directly to the main principal or dean of your school. Let him/her know that you have confronted the teacher directly and have gone through counseling department but there is still a problem with a teacher behaving inappropriately and harmfully.
*Get your parents involved if you don't think you can handle it on your own. Keep in mind, though, that you will benefit more in the long run by handling as much of it as you can on your own. You need to learn these skills. Let your parents know at first that you would just like some support and encouragement. If the adults at your school aren't helping you, though, your parents may need to step in and help more directly.
*Witnesses or peer support will be a great aid. Do you have friends or neutral classmates that have seen this behavior firsthand? Would they be willing to share their observations with counselors and/or principals if necessary? Even if all your friends aren't in that class or have never seen this behavior, at least let them know you're fighting this battle. Your friends' job is to stand by you and support you. Give them the chance to.