"You are tutoring my daughter who you have become so sexually attracted to that you have openly told me that you fear might rape her. But she's doing well in her studies, so pretend that I'm her and fuck me instead!"
...So the right thing to do is to be frank about your desires and confess to the mother about your desire towards her daughter who is your student?
Well, they do say honesty is best.
That's one way to do it.