Is the antagonist a bad guy?
We could aim the question back at you, Glinda.
I do think The Wicked Witch of the West was crazy and had a mean laugh. And for me as a child she was at the top of the list for villains. She was Dorothy's antagonist.
Dorothy's wanted to get home and according to Glinda she needed to visit the Wizard. The Wicked Witch of the West didn't not want her to meet the Wizard, and the movie never tell why. Since they're desires are against each other they are each others' antagonists and Glinda and Dorothy are allies.
While Glinda is not Dorothy's antagonist I wonder if she is the story's bad guy. I once heard or read that the true villain set the story in motion. Glinda knows that Dorothy wants to get home and the red slippers on her feet the whole time she skipping down the yellow brick road have the magic to send her home from the beginning but instead she send her down a path that leads to murder. In the end Dorothy goes home with blood on her hands and Glinda stay as the most powerful person there and therefore rules Oz.
All this is not to change the way you watch Wizard of Oz or the way you look at the Good Witch Glinda, but it's another thing I learned from writing my 2nd YA novel you need to have an antagonist (which my novel doesn't) and you need to know all your bad guys.