Wow, this is tough, and I am not there yet, but I think there comes a time when still telling her that when SHE is asking is doing more harm than good. I distinctly remember nagging my mom about that age (and yes, right before Christmas b/c my friends talked about it at school and church...). She sat me down and told me that "Santa Claus" wasn't a real person, but about the spirit of Santa and how important it is to give and make people happy, blah, blah, blah, and even though it was "ruined" for me that year, we turned it into a celebration of me being old enough to know the truth and I got to help do some special Christmas, Easter and Toothfairy things for my younger sister. After the initial crying about learning the truth and feeling lied to, I was actually proud to know my mom thought I was old enough to handle it and felt like I knew the "secret" from then on.
I know that may not be what you need to hear, but 8 is not too young to understand lying and she may resent you for making her feel stupid or naive around her friends if they already "know the secret". I think you should use it to your advantage to create a neat and special bond between you two this season instead.
Good luck with whatever you decide though...