I really really hope your mother will come around. I've dealt with religious fundamentalists in the past (for different reasons) and sometimes it's like talking to a brick wall. I've been told that I am going straight to hell for eternal torture simply because of my political affiliations. Many are set in their ways and are unable to consider different perspectives in life. One angle you might want to use is to say that god made you and this is part of his plan. I find that many deeply religious people are fatalistic and enjoy hearing that we all have a plan made by god. If you can convince her this is part of gods plan for you, it might be easier for her to accept. This would be a good move for your therapist to take. I wouldn't focus the argument on the evidence supporting GID, but rather make it an emotional appeal to her spiritual beliefs. She may just reject any evidence for your condition, but she likely won't reject this if you can convince her this is god's plan for you.
Once again, I wish the very best for you. I hope she comes around.
