I ordered Lands' End sandals for my DD last winter (for our WDW trip of course! ). I measured her foot per their instructions and the sandals ended up being at least a size too big. Luckily, we had other shoes for her and she only had to wear the sandals to dinner.
Did it say anything about that in the description? I have found that they are very helpful with size questions by e-mail or phone. I would say next time you see something, contact them first.