My know-it-all

I live with a little know-it-all. And I just think, it must be nice to be 8 years old and already know everything there is to know. She's just so brilliant, so wise, I'm so blessed to be living with such a genius, who needs friends or family to counsel with or the internet or books when I have the fountain of all knowledge living with me???
She's driving me crazy!!
"Mom, next time do it this way."
"Mom, are you sure we're driving the right way?"
"Mom, you did that wrong."
And she looks at Chad and me with such skepticism and doubt whenever we tell her something, "do you really know what you're talking about?"
She questions EVERYTHING we tell her or ask her to do. "Why?" "How?"
Aaarrgh!
I finally sat her down today and did a little 'tooting' of my own horn.
"Do you know that I'm actually quite smart, Debbie? Do you know that I got straight A's in school? Do you know that I got a scholarship to college? I AM A SMART PERSON and I know what I'm talking about so stop being rude and questioning me and dad all the time."
We'll see if that works. But I am so sick of it. I'm tired of her little smirk and her attitude and her disrespect. Something needs to change, because if this is how she treats us as an EIGHT YEAR OLD, how will she treat us when she's a teenager????
She has an excuse for everything, we'll ask her and ask her and ask her to do something and she blows us off and then gets mad and indignant when we finally get angry and yell at her, like it's our fault she didn't listen. What am I doing wrong with this child?!?! And if she can't take responsibility for not picking up her dirty clothes or for not listening and obeying when we ask her to get dressed - things that are obviously completely HER responsibility - what's going to happen when she starts making big mistakes?? Am I raising a serial killer??? Most likely not, I know. She still a pretty good kid, she's just got an over-inflated opinion of herself and is developing some bad habits and I just need to figure out how to help her. So, if anyone has any suggestions on how to teach children respect and responsibility, I would appreciate any help.