My child is an atheist. How did this happen when I raised her as a Hindu Brahmin?

I'm guessing that your child is of some age now to be talking about this. What I can say is: 1) Respect whatever your child believes in, even if it's not the same as yours - that's the best thing you can do as a parent. Be it religious beliefs, aspirations in life, what she loves to do, things she likes - please, please, please give her the support! 2) Don't force your ideas on her, and respect those differences - she probably doesn't get in your way with her beliefs, so don't get in her way with yours.