Glinda the Witch can be found in the witches cave along with Small Nose Nelly and Spikey Sarah. The Witches cave is located in the desert biome on the other end of the railroad tracks.
Glinda offers you a quest that eventually rewards the witches brew potion. Glinda can also offer you daily quests that give gems.
She was also the main character in the Boxing Gloves quest which you need to complete in order to get access to the Boxing Gloves ingredient.
She will most likely be a main character in future quests on Wacky Wizards.
Glinda was introduced to the game on the July 7th, 2021 Wacky Wednesday update.