Can someone help convince my sister to wear sneakers to an amusement park?

She is 10, so she's at that point where she thinks looks are everything. She wants to wear sandals to the park, which i say is a horrible decision. I keep telling her that her feet will hurt but all she says is "no they won't, and I'm not wearing sneakers! They won't go with my outfit" and stuff like that. How can i convince her that looks aren't everything, and she should wear sneakers? I even told her that no guy will even look at her. (For some reason, she thinks the place will be crawling with hot guys who want to "hook up" with her, which is total bogus) I wanted to just let her suffer, but I don't want to hear her complain the whole time, plus that would be kinda mean. My mom refuses to buy her a new, comfier, pair of sandals, and has tried to reason with her, but my sister just storms away. Help, please!