I live in flip flops as well. (Same as another reviewer, Teva Mush, Sanuk Yoga Mat, Reefs etc!) I can't do sneaks in WDW. Way too hot for me!! I have found that Clarks makes pretty cute flips that have great arch support. Reef does make a flip called the Slap. They are very cushy and comfy, although not all that supportive.
If you go to footsmart dot com you will find a TON of foot and arch friendly shoes from sandals on up. All the best brands live there!! Let your daughter have a look. She'll find something!! Montrail Molokini are SUPER comfy and supportive but I found that they are pretty clunky looking if you have small feet. I looked ridiculous in them, but when my sister tried them on they looked great. We wear the same size but she is much taller than me and somehow they looked better on her "tall person" feet!

She stole them from me and tells me all the time how amazing they are!!! Your daughter may have try on a few before she finds the right Disney foot wear!!
good luck!!