A.J.
First of all, she's 6, and you're her mom. Don't let not wearing socks be an option. Tell her that with sandals she doesn't wear socks, but when she puts shoes on, they are a must. Make it a rule. Second, I would get rid of the shoes she has and buy new ones. In my experience, you will never get rid of that smell, and even when she puts clean non-stinking feet in them, her feet will stink afterwards just because the shoes are stinky.