I definitely recommend that you do your exams and focus on that. Any Dom/Domme worth his/her grain should support you in that decision.
Talk to her. I am sure she understands your position and that this is something you feel you need to do. There is a time for D/s and there is a time for R/l and they cant always be one and the same. It is not dishonesty with her unless you dont tell her an just ignore what she wants. An open discussion is the key here.