How do you maintain a good relationship with a parent when you have conflicting religious views?

First off, I don’t mean to offend anyone with this post and if I do, I am sorry. I was baptized and raised roman catholic, but ever since I was old enough and I had time to develop my own views, I have been atheist. My mom is a strict Catholic and she is very upset and offended that I am, in her words, rejecting her religion. I think she thinks that since I was raised a certain way, I should practice it. I don’t think she understands that even though I don’t believe in God or Jesus or Heaven, I am still a good person. I find that my mom and I have very similar morals – just a different view on religion. So why is it so important that I believe in God? I never bash her religion, if she wants to be Catholic, that’s fine. I have NO problem with Catholicism, or Buddhism or Judaism, whatever. I just don’t believe in God. We’ve been arguing a lot lately over this issue… and I’d really like to put an end to it and have a decent relationship again. Any advice?