have you considered going down the "What do you think, sweetheart?" avenue?
That was my first thought as well. I'm not a parent, but I am around a number of cousins and such with young kids. I may kind of answer both fo the popular ones here and say, "That's a question a lot of people ask, and no one really knows. What do
you think?"
From there, you follow where she leads, rather than trying to blaze the path yourself. You'll be able to make sure your answers are at the level she can underatand, and more importantly, at the level she expects. If she's hoping for a quick answer and you launch into a history lesson of the Hebrew people through the early Christians and Romans, she may decide not to ask you such questions in the future cuz "you're boring."