>>37007610I'm guessing she was added to be a mini-tutorial on the Fairy type for people returning to the franchise who won't be familiar with it, since they didn't have to worry about it on their original Kanto playthroughs. Valerie is said to come from Johto, so whether or not they'll have her serve a similar role in let's Let's Go Pichu and Togepi I can't say.
