I do not own nidalee, however playing against multiple ones, I've noticed something.

Whenever she gets a cs, you hear this "woosh" sound and then leaves fly around her. I looked at her skills on wiki/JabeBot and nothing was said about it

Does this do anything? Or am I just completely blind and missing something obvious.

I think you might be just hearing the animation for her "obtaining" a new spear to throw at you.

I guessed so, I guess I'm just crazy and only see it when she gets a CS.

Thanks qt3.14

You should probably just play her to find out. I dunno about others, but I cannot figure out for the life of me what sound you're talking about.