If she put the jumper on after SS left then the footage LE has with her wearing it would make the last confirmed sighting later than what they are saying?Teenagers are not very good at keeping secrets usually. Especially when pressure is applied unless they have experience with that, like growing up in rougher neighborhoods or constant run ins with LEO. BUT, they might have more confidence in their decision to stay quiet if they have adults coaching them. An adult could be worried about their child's future, or their own future. Like the Jello shot thing, if my kids are cooking something in my kitchen I am pretty sure I would notice them adding extra ingredients. So was that provided by the owner of the house? An older sibling? Other relative? Could one of the attendees, have a parent that had unprescribed pills and they stole them bringing them to the party? Just my wild ways of thinking I guess.
I also thought it was weird that SS did not remember the white hoodie though... Unless KR put it on after she left or before they met.