If you knew you could hurt your mother emotionally by telling them something what would you do?

Having been in this cirstance, I would do a combination of A and B. You should be very clear about your stance regarding her behaviour and not participate in your mother's denial. On the other hand, she will probably not change, it is really between your mother and her grown son, and the sad truth is that, should you pursue C, the odds are that EVERYONE will turn on you. The messenger of these things usually "gets shot."