how do baby showers work?

One of my very close friends is due in a couple of months. She's my first close friend to be having a baby, so I haven't yet been to a baby shower. As one of her closest friends, am I the one who is supposed to be initiating / planning a shower (if she even wants one)? Or does someone in the family usually do that? I know I could just ask her, but figured I would ask here first in case anyone knows what tends to be standard!!