Is there another place you can go to?
She could have meant that he wasn't happy because he didn't have a happy face on in the car? Which is silly because no one just walks around with a frickin smile on their face all the time.
I can't stand when people point out the obvious, like "you have acne" like she did. I would have said something like "and you have squinty eyes and talk funny." I know, not very nice, but that's one of my pet peaves. I always get the "you have baby nail." I'm like "yea, I have small nails, so don't mess up!"
Nothing she said or asked is really any of her business, I'm sorry you were put in an awkward situation. It may have been her idea of "girl talk," but she's you're nail lady, and should just stick to doing nails and talking smack in chinese in front of you to her nail lady friends.
If you go to her next time and she brings up something else that isn't her business, and make you feel uncomfortable, don't be shy to tell her that's private stuff.