It's true that in the Wizard of Oz it was Glinda, but 1) I can't find it here and 2) If you pronounce it the difference is very small. Sorry for my English:)
The only Glenda I've ever known was named after her father, Glen. I don't like this name much, because it reminds me of the famously awful movie about cross-dressing by the famously awful director Ed Wood called "Glen or Glenda?"