That was the biggest change between the MGM movie and the book. ITB, after her witch-squishing, Dorothy was met by the (unnamed) Good Witch of the North who sent her on her journey. She didn’t tell Dorothy about the shoes because she didn’t know.
After being left behind by the Wizard’s sudden departure via balloon, Dorothy is told that perhaps Glinda, the Good Witch of the South might know another way for her to get back to Kansas. After another round of adventures, she meets up with Glinda who, being wiser than TGWotN, knows the shoe trick.