Dorothy and Aunt Em don’t actually have a conversation in the first chapter. Aunt Em just calls out, “Quick, Dorothy! Run for the cellar!”
The first woman (or character) Dorothy has a long conversation with is the Good Witch of the North, and that conversation eventually focuses on a man: the Wizard.
In her journey to the Emerald City, Dorothy talks with two more female characters: the Queen of the Field Mice and a housewife outside the city. But they both talk about the scary Cowardly Lion.
In the city itself, Dorothy chats with a young maid in the palace; later Baum named this character Jellia Jamb. They discuss clothes and the Wizard.
Dorothy then sets off to kill the Wicked Witch of the West. The Witch captures the little girl with the help of her winged monkeys, and at last there’s an extended exchange of words that’s not about the Wizard or the Lion. So in chapter 12 The Wonderful Wizard of Oz does indeed pass the Bechdel Test. Of course, the conversation between those two female characters is all about shoes. (Way to undermine the stereotype!) And it doesn’t end well for both parties.
Glinda and has a really substantive conversation about her adventure, who should rule parts of Oz, and how to get home.
By that point in the book, the Wizard is no longer a factor; both his humbug magic and his shaky ballooning skills have come up short. Dorothy has learned to stop relying on that man.
That’s when The Wonderful Wizard of Oz gives up the pretense of revolving about its title character and focuses on its real center: the change Dorothy unleashes everywhere that she and her companions go. That’s one reason I think the book’s final act, which can seem like an anticlimax, are in fact crucial to its tale.