Hmmm every case is singular, but I'm tell you my sincere opinion:
If you are not planning to transition, then perhaps you don't have necessarily to tell your mom that you are transgender. Considering your mom as a religious person, she might have difficulties to understand and accept you. We can't know how will she react...she can accept you and great! But she can have a hard time to understand and, in this case, from this day on you will not be seen anymore as the person you were. She can change the way she treats you and not for the better. Once you depend of her financial support, it might be better if you avoid this kind of conflict right now. It is a great risk and you need to see if it is worthy and necessary.
But, at the same time, if you are not planning to transition...then telling her should be quite less impactant than telling her that you will become her daughter
I only told my mother when I was already on HRT and only after a lot of time thinking and fearing about her reaction. I am in the middle of my transition, so telling her was a need. I was already presenting noticeable changes and I couldn't stay anymore in boy-mode with her. I needed her to know because I needed her support.
Initially I got terrible reactions from her and from my grandparents (my mother told them). Right now my mother is almost accepting me, but my grandparents stopped talking with me and they think I am some crazy pervert...they are making every single effort to discourage me about it. I was extremely close to them, almost like I am with my mother...but now I feel I lost them...
I don't want to discourage you, but you have to know that telling your parents is very risky. But, on the other hand, there are a lot of girls here that had excelent reactions from their families. I think it is almost a lottery. You can't predict.
So, my final advice is: think really carefully about it and see if you really need to tell her the hard thuth. If your problem is depression, then you might give her a few hints about the reasons not telling clearly and openly that you are transgender.
I hope I have not messed up with your mind, but I am being sincere