Your own personal well being is of the utmost importance, it might feel as if you're hiding who you are from your family by not discussing this with your parents, but you have an awful lot to lose if you were to be disowned.
I would suggest to find a community (such as ThinkAtheist) to discuss the troubles that you have, I'm sure that many people can give you support and comfort that your parents can't give you.
Personally, if I were you I would wait till you're less dependent on your parents for financial support to come out of whatever closet you're hiding in. It's a pity that you feel that you can't be who you are around your family, whether it is true or not that you might not be able to, the feeling that you can't does seem to me to imply that you fear that your mom is basically a bigger supporter of baby Jeebus then her own baby (you)?
I wish you the best, both in family and in love. You're young, you are finding out what it means to be "Becca", you can hide who you are from your family, but I would recommend to find people to talk about your feelings so that you don't have to hide to yourself who you are. Expressing how you feel and think are vital to your development, I do hope that ThinkAtheist can help you by providing you with a sense of community.
I'm considering opening up to my close friends, only one knows so far and even though she disagrees she supports me and that means a lot.
Becca, you seem like you've got this figured out fairly well. I'd like to offer one additional bit of advice, which you may have thought of already, but in case you haven't, here it is. The people you consider to be your close friends may change, and that change could happen abruptly and for less than pleasant reasons.
Why do I mention this? When I was your age my good friend Tom, who was raised as a Pentecostal Protestant, began to have doubts about his religion. (And that is putting it mildly.) He shared these doubts with me and a handful of other friends from school, including his good friend and next-door neighbor Harold. Like you, Tom wasn't in a position to rebel openly, so he rebelled privately and in the company of those he trusted.
Skipping ahead, Tom and Harold both ended up liking the same girl: Cindy. The week before junior prom, Harold had a conversation with Tom's mother, during which he turned over the music CDs, comic books, and other items he was holding onto for Tom. Harold showed up at the prom with Cindy. Tom didn't show up at all. The rest of us rarely ever saw Tom outside of school again and when we did see him at school he didn't look very happy. Harold insisted he had done it for Tom's own good.
Be aware that telling someone about your atheism means you are irrevocably granting that person tremendous power over your life for many years to come. It might seem unthinkable that someone you know and trust would ever hurt you deliberately, but that is exactly the reason why you should think about it carefully. That goes especially in dealing with friends who disagree with your atheism and might one day decide to take similar steps for "your own good".
Good luck, Becca.
Has she ever discovered some friend of hers was not of the right religion? If not atheist, then some different sect, maybe very different, or perhaps agnostic?
If so what was her reaction? It will be worse when it's her daughter and it's atheism, not just her friend Katie being a Mormon. If the reaction is bad, she might let the blood relationship overrule her desire to disapprove violently. But I would not bet on it. Atheism is way beyond the pale for many religious people.
Even if she did decide not to disown/shun you, then you can expect attempts to evangelize you for the rest of your life.
Lesson for life: Religion causes segregation and discrimination.
I agree with your decision not to come out until you move out. I haven't officially come out to my parents, and I'm 32. I think they know, because of the opinions I have about related topics, but I don't see any point to sitting them down and saying "I'm an atheist".
Love your family, and when they talk about their silly beliefs, laugh at them silently, but love them all the same. It's a shame you can't expect them to laugh it off if you came out, but we all put up with a lot of crap when it comes to family.
I am going to tell you what I told my younger brother when he came out to me--
Don't tell your mom until you are able to live on your own.
There is always a chance that she will be accepting and kind, but it's also possible that your life will be made a living hell for the next few years. It's a shame that you have to do things this way, and that you can't be honest about who you are right now. Luckily, you have access to supportive communities of people elsewhere. I hope this will help you get through until a time when you are able to come out to your mom, and I hope she accepts and loves you for who you are.
You have an entire website full of people who see eye to eye with you. From the statement your mother made, I am going to assume that she is rather right wing and conservative. When you are 16 you are sort of dependent on your parents for support, shelter, food, etc. Sometimes a parent will abuse this and make it seem like they "own" you. I understand that this can be extremely frustrating. I have been in a similar situation, but trust me it will get better. If you cannot come out to your family, find a friend that you can trust with anything and talk to them. Having an outlet can be very relieving. I understand that you object to your families beliefs, but why? Get a notebook, or an online blog, and investigate all the beliefs and think about why you object to them. This too can be quite liberating, especially when people comment and agree with you, or give you more information. Learning, although difficult, is liberating and gratifying. Knowledge is power.
Good Luck to you!
There's no reason why you should tell anyone at all even after you move out. It's not important