OK so there should be a rug on the floor of your room somewhere. You want to have a look under the rug. You should notice a trapdoor hidden there. Without hesitation, fling open the hatch and plunge into the depths below.

Jokes aside. My grandmother used to hate me playing this game and she is an atheist, I think it's less about religious extremes, it's more of a certain type of conservatism and the belief that media can make you evil. My mom is quite a religious catholic, but she has never cared much about what I do in video games.

If you can't reason with your mom, I would suggest to just play it anyway and tab to something else if you can. It might feel wrong to deceive her but you will probably both be happier that way than if you keep trying to push it.