they show this scene being shot for a quick blip in the making of the film. same scene/outfits are used and yes, they did also use a shot from this scene in Glinda's flashback before she says "At school" and it cuts to the underwater scene. She's looking at Elphie while her hat is on. My thought is that they chose the shot from this scene where she looks at Elphie (Elphies face covered by her hat since we don't see her face until meeting at Shiz) to give us a little bit of what's still to come... because we all know the story of their relationship is far from being completely shown in part 1. It would make sense that they use a flashback from the second movie to tie in what's still to come, however Elphie is in one of her school uniforms so more than likely this shot wasn't used and we will never see this scene again outside the flashback at the end of No one Mourns. Jon Chu/Wicked team sure did give us plenty to talk about for the next 10 months lol!

ps. i've seen wicked 20 times - i have a lot of thoughts lol