A.,
Start with the most basic answer you can give. As she asks more questions, give her simple answers. She will ask questions only to the point she can handle the information.
At eight, she is probably not able to handle the entire picture, but it is important to give her answers. If you give her more information than she can handle, it may be difficult for her to deal with.
You didn't specify as to what the question was. If it was "Where do babies come from?", you could say "When two people care so much for each other that they want to have a baby together, they have sex to try to make a baby." This may be enough for her -- at least for now. If she is looking for more, she will ask for it. Just answer questions as simply as possible, and let her follow-up questions guide you to the exact information she is looking for.
I know how ackward this can be. As a single mother, I had to explain erections and wet dreams to my son. Not the easiest thing in the world, since I have never experienced either one. I gave him short, age appropriate, answers. He wasn't looking for a biology lesson, just why he had them and if they were normal.
Good Luck. You will be fine. Just try to hid your discomfort.
M.