Well, you've learned the truth about the truth at a young age, so congratulations, you're in a much better position than many on this board that have wasted decades before they realized the truth.
Also, I totally respect you for caring so much about your mother's feelings. The sad thing is that she is trauma-bonded with the religion. It's the thing that gave her solace when she was going through a very difficult time.
However, she made a bad decision. The people she trusted hurt you. Does she know this? Maybe she should be made aware.
Her reaction could go in any number of ways. She could be angry or she could disbelieve or it could entrench her further.
At any rate, why protect her from the knowledge of her own bad decision?
I think it is hurting you more than you know.