I feel it’s best to just be honest about everything right from the start. It all depends on your religion too of course, and what you want to pass on. I feel christianity offers me an easy way out. She can discard it later, but for now I just tell her that people have a soul which will go to heaven and meet other dead people and be happy, whereas the body is no longer needed and that’s why we bury it. And that people we love always remain in our heart.