Oh, and to be canonical about the first book (for those who haven't read it):
Dorothy never comes face to face with Glinda until the penultimate chapter.
When her house lands on the Wicked Witch of the East, she is met by the unnamed Good Witch of the North
. The Good Witch of the North doesn't know how to get Dorothy back home, so she turns her hat into a slate, on which words magically appear, directing her to the Emerald City. When she is captured and enslaved by the Wicked Witch of the West, the Witch, in an attempt to steal the Silver
Shoes, places an iron bar across a floor Dorothy is to mop, and renders it invisible. Dorothy trips over it, loses one shoe (which the Witch promptly snatches up), and (in a fit of unthinking rage) dashes the contents of the scrub-bucket over the Witch, who collapses into a puddle over the course of about a minute.
It's only after the Wizard's balloon breaks its mooring ropes, leaving Dorothy still marooned, that the Soldier with the Green Whiskers finally suggests asking Glinda for help.