I can't verify where Millie Bobby Brown wore this outfit, but I am going to guess Coachella. The only thing it might be missing is the flower crown. Doesn't it feel like there is a designated outfit for coachella? LIke a memo went out and told everyone how they should dress. Imagine showing up to Coachella in anything other than a flower crown? They'd kick you out.
Stranger Things Fact Number Thirty Six: One of the most interesting relationships in season two is between Eleven and Hopper. In one key scene, Eleven acts out as any teenager would. The only difference is that Eleven has psychic powers that slam Hopper into the wall and send things flying across the room. Hopper actually did his own stunts for that sequence. I really appreciate that, even if his body might not have appreciated it.