I am performing my job, but I am worried that if things go bad with us she'll claim sexual harassment. What should I do?

Don't let things go bad. I.e., stop talking about sex, try to hide your feelings, don't flirt, etc. As long as she is in your class, you have a professional obligation to treat her the same as your other students, regardless of whether she welcomes your interest. Doing anything else is dangerous. (Even if she makes no complaint, other students may raise the issue with the administration, if they are upset by it or suspect favoritism.)

In principle, you could try to change your teaching assignment to another class. However, I'd strongly recommend against asking for this. It might not be possible (maybe there's nobody available to switch with you), in which case you'll be in a real mess if you have implicitly announced that your current assignment is untenable. Any changes will be disruptive, which will annoy the professor teaching the class as well as whoever handles the teaching assignments or has to switch with you. Plus the teaching change will be public enough that it will probably create rumors of impropriety.

En tant qu'étudiante qui est actuellement TRÈS intéressée par l'un de ses AT, je dois être d'accord avec ce que tout le monde dit: FAIRE. NE PAS. ENGAGE ...

Attendez que vous ne lui appreniez plus (et il n'y a aucune chance que vous lui appreniez plus jamais), alors n'hésitez pas à accepter toute invitation à prendre un café. Lui demander de prendre un café vous-même pourrait être risqué, s'il s'avère qu'elle n'est pas aussi intéressée que vous le pensez.Si elle vous aime autant que j'aime mon TA (qui a inconsciemment aussi manifesté de l'intérêt pour moi, mais a fait très attention à ne pas montrer cet intérêt ... Je n'ai aucun moyen de savoir s'il est réellement intéressé avant la fin du trimestre, quand je prévois de lui demander de sortir), alors elle vous demandera de sortir après la fin du trimestre. Si elle le fait à l'avance, expliquez-lui poliment que ce serait tout à fait inapproprié.

À ce stade, il n'est même pas judicieux de lui dire d'attendre la fin du trimestre, car vous impliqueriez toujours que vous l'aimez. Vous devez agir sans intérêt jusqu'à la fin du mandat. Période. Elle l'obtiendra. Et elle attendra. Soyez patient et ne soyez pas obsédé, sinon cela se verra.

Under the assumption that you're in the US, it may be the case that you've already violated your school's policy on sexual harassment. It's important to recognize that quid pro quo harassment does also constitute sexual harassment under most (if not all) school harassment policies. Simply put, quid pro quo harassment occurs when a person incentivizes engaging in sexual or romantic activities with him or herself in the workplace. Again assuming that you're in the US, quid pro quo harassment is most likely prohibited by your college's sexual harassment policy. Title IX generally requires college's to have such policies.

As someone who is in a relative position of power over this student, any attempt to initiate or maintain a relationship with her is almost certain to be a violation of your school's policy, and could end up having quite serious implications for you, regardless of how your hypothetical relationship plays out. While you may view this student as being the initiating party, as the person in the relative position of power, it's your responsibility to set boundaries.

From your question, it's not clear to me exactly where you are getting the idea that this person is interested in initiating a relationship with you, so I would avoid broaching the subject directly, however you need to stop any further discussions of the sort you mention as soon as they come up by saying "I'm sorry, but that's not an appropriate topic for us to talk about". It isn't exactly what you're asking, but I can't help but notice that I don't see any evidence from your question that she's actually interested in having a relationship with you anyway. You say that you had a conversation where sex was mentioned, and that she touched your arm once. Neither of those things to me necessarily imply "interested in starting a relationship", though of course there may be other reasons that aren't in your question.

Other commenters here have suggested trying to switch teaching assignments, however I would suggest that that will not entirely mitigate the power differential necessary for quid pro quo harassment to occur. The best way to prevent her from claiming sexual harassment, is to not commit sexual harassment. It's not the answer that I think you want to hear, however it is the answer that you're likely to get from your school's HR/Title IX department.

Parlez-en à votre professeur. Selon le cours, le professeur peut avoir une certaine marge de manœuvre pour demander à un autre assistant technique de prendre en charge le classement de son matériel et ses interactions avec elle, etc.

Et sinon, il serait bon d'avoir vos préoccupations "sur l'enregistrement."

Vous avez tout à fait raison d'être concerné, mais vous n'êtes pas obligé de prendre des décisions (sur la façon de gérer le problème) tout seul.

In addition to Anonymous Mathematician's fine answer, I'd also recommend that you also take steps to make sure that all of your future interactions with students are in public places where witnesses will be present. For instance, hold office hours in a library or café instead of in a private office. Note that this would be a general policy for all of your students, not just your interactions with the student in question.