I think the appropriate ethical guidelines that apply in who a therapist can accept as a client (as opposed to the ethics of therapy itself or relationships afterwards) is whether there is a conflict of interest here. Once you are no longer a student, I don't see how there is a conflict anymore (or a dual relationship). You might ask whether seeing her as a T might prevent you from taking other classes with her, should she teach them and should you want to. Otherwise, do what seems right for you.