@Legion It's a difference in walking style brought on by the difference in material and construction. Most flip-flops, sandals, and slippers are semi-flexible and allow you to use your normal gait, with maybe only a slight change to ensure you don't slip out of them. Geta (what she's wearing), on the other hand, are rigid and inflexible, so they require a different gait to walk in, which most aren't used to, since geta are typically only worn with yukata, which are usually only worn during festivals.
Additionally (and, really, more importantly), because they're worn so infrequently, it'd be like trying to break in a new pair of shoes that you've never worn before by participating in a 1k marathon.