You are already coming up with honest and spirited responses to her comments. I think you're doing about all you can, and I'll bet as long as you treat her as if you like and respect her, she will continue bringing her honest comments to you. She could even be bouncing them off you to get an additional perspective.
Isn't it interesting how kids mirror what they hear/see in adults? I'll bet she carries some of your comments home to her mom, to see how SHE reacts. She sounds like a bright little girl, and will probably figure out many things for herself by the time she's grown up.
I'm just remembering that when I was 8, I used to dream out loud to my mom about the fabulous, huge horse farm I was going to have some day. Miles of lush, green pasture, crisp white fences, big beautiful stables, and of course, the best Arabian and thoroughbred horses anywhere.
My mom kept throwing out all these practical objections about money and labor, warning me not to get my hopes too high, telling me I'd probably be a secretary or housewife, etc. I was always so disappointed that she could never just listen and support my dream.
Of course the dream would (and did) change as I grew up and learned more about reality. But my mom lost early, or never had, the ability to just let my thoughts be my thoughts, and by the time I was 11, I recall clearly thinking that my mom was never on my side, so there was no point in ever telling her anything again.
I guess I relate that story because it seems to be the other side of giving good, caring advice. If adults listen with heart, children are quite capable of figuring many things out themselves. Following this leading, I've really enjoyed the books Raising an Emotionally Intelligent Child by John Gottman, and How to Talk So Kids Will Listen, and Listen So Kids Will Talk by Faber and Mazlish.