I'm assuming you've tried boys shoes? All of my kids/students are wearing Vans and the boys/girls shoes look the same (they might even be the same). Other casual choices in boys that work on girls are any of the Nike free sneakers or Adidas samba (they didn't even make a girl version of that for a long time and girls wore them anyway). Sperry docksider style in boys sizes might work too.
Also go to longtallsally.com or zappos.com (half sizes are tough, but could you use an drug store cut to fit insole?) for ballet flats and ankle boots.