Nope none at all.
This teacher is having sex. Lots of teachers have sex. Some teachers have straight sex, others have gay sex. Some teachers have more sex and some have less. Some teachers indulge in practices that are different from what you do. And apparently some are getting paid to do this. In the end it is none of our business so long as they are getting the job done in the classroom.
Some of the pupils fathers may well be her clients as are men in a whole variety of 'respected professions.' But hang on. We never talk about the customers do we, just the prostitutes and their morality.
*Bangs head against desk*