When Effie and her friend, Sarah, dive to the bottom of the bathtub, they find themselves in the ocean, where they meet the owl and the pussycat sailing to the land where the bong trees grow
This is the one with the OWL AND THE PUSSYCAT tie-in — the two girls are invited to the wedding.
I chose the name Effie for one protagonist of the story because, after reading (or being read) a book called EFFIE AND THE DRAGON (?), Jesse "changed her name" to Effie for several months. And Effie was the name that Jesse and her husband chose for their first child.