I was thinking about the fire featured prominently towards the end of the reveal teaser trailer. One of the girls seems to be desperately trying to open a jammed door on some kind of building - I assume in the woods - maybe a cabin of some sort? It could be that the girls played a prank on another girl or a boy maybe, locking them in the cabin, and then a fire starts and they’re not able to get them out in time and that person dies.
They then obviously hide any evidence and make a pact never to tell anyone what really happened. I know it doesn’t really have a supernatural angle though so it doesn’t explain the purple glowy thing lol but what do you guys think?