As an ex-Muslim myself I can attest to the extreme isolation you can be forced to feel when leaving the religion. I'm convinced it's just a way to get people to stay within the faith. If you are not financially independent you may need to keep up the prayers just until her cutting you off wouldn't have anything more than an emotional toll on you. I can only speak from my experience, but I have found Muslims to be the least accepting of Atheist thinking of all the religions. It's a rather strict religion, and the penalty for apostatising is usually just as severe as you'd expect. My best advice would be to bite the bullet and keep peace with your mother, but to also start actively working towards being financially independent. Once you leave your family home it makes it easier to make the decision of telling your parents. You can either live like an Atheist in private, but keep up the facade of being a Muslim around your family (I know quite a few people who do this, girls wear hijab at home, but not out etc etc) or you could tell them. At that point its an easy choice because you simply do what you feel would be the best option. No pressure about worrying you'll be homeless, hungry, etc.
Good luck. Islam sucks.
Good luck. Islam sucks.