candydog2 said: "
I think it's like a combination of magic and mechanics. Sort of a mechanical invention that could only work with magical help."
Which also ties in to the source material and Maguire blending magic, religion, and engineering (Tik-Tokism) throughout Oz.
For those who asked whether it's addressed in the novel, it's not, as Maguire doesn't mention Glinda traveling by any magical means. Though she does have a lot more magical power in the novel (she's the one who's studying sorcery in Shiz, Elphaba specializes in life sciences; Glinda is the one to place the enchantment on the silver shoes), she's still not considered a particularly powerful sorceress, just more of a relatively well placed member of the upper class. He has her tell Elphaba that she was already in Munckinland, about a dozen miles away, when Dorothy's house dropped on Nessa, and that she traveled to the scene quickly via Pfenix.