Kenpachi made Kazuya's theory on how hurricanes work and the best way to stop them known, though he didn't tell her that it was just a theory but talked to her like he was absolutely certain of what he was saying. Kazuya most certainly came from another realm, and based on the circumstances surrounding him, everything he is certain about always worked out. So just like Orihime, he had a blind yet assured faith in Kazuya's words.
"Fine," Rangiku conformed with a shrug, "it's not like I was making any progress on my own anyway." "Let's do it."
Kenpachi looked at her for a few seconds in awkward silence, expecting her to give her order, forgetting that he was the one who came up with the outrageous idea that they were about to try out. So he was the one who was supposed to be leading the way, not her.
"What are you waiting for?" she asked him. "It was your idea, wasn't it?" So lead the way!