The term apostasy is used by sociologists to mean renunciation and criticism of, or opposition to, a person's former religion, in a technical sense and without pejorative connotation.
http://en.wikipedia.org/wiki/Apostasy
Don't feel you have to tell your mother the whole truth. This religion has lied and lied to innocent people raised from childhood in it. Be wise and be a loving daughter, choosing your words carefully. You can't tell a brainwashed person the truth, not yet. Please tread carefully.