I am sorry that your mother is putting so much pressure on you. Unfortunately she is going into full cult mode believing this emotional manipulation and blackmail will bring you to your senses and you will come back to God's loving organisation. She cannot see that her unloving and aggressive response to your emotional and spiritual dilema is confirming your doubts.
At the moment she is trying to manipulate you herself when this doesn't work she may decide to go to the elders. Certainly her message suggests that she has total faith in the organisation. She has no appreciation for your perspective or your emotional well being and as you are no longer one of the faithful she will not even consider what you want or feel.
Whilst she is coming to terms with the situation I would keep your distance from her and limit contact. She is currently unstable and when she cannot influence you her attention will turn to her grandchildren, certainly they do seem to be a preoccupation in all her messages.
For now I would focus on your family unit preparing and building a life that will allow a smooth transition from the cult life to a more normal one. As you seem to be moving towards an end game take control of those elements of your life your have power over.