This is my Theory at the moment (anyone else kind of here)
1. LS was having a night of badass fun ( bunch of guys, alcohol, coke maybe xanax, pot, some or all of the above, she chose. (Not judging, I've been there.)
2. LS and CR went to Sports to see who was out or to pick up something to refuel.
3. They went to Smallwood to get someone or something else and LS & CR thought they would go back to Sports, no idea it was so late.
4. CR runs into or is followed by someone with whom he had differences.
5. CR decides to return to 5 North to get away from angry pursuers rather than back to Sports
6. LS intended to go back to Sports with CR but is too messed up to think, "oh he's going home, I guess this is where we say good night" and just follows CR not knowing what she will do when she gets to 5 North
5. Something bad happens at 5 North, could have been alcohol poisoning or coke heart-attack or something else. As HS students, these kids have been lectured by their parents not to party in the parents home because the parent could be held responsible if something bad happened. So now, something bad happens in their own home and their instincts tell them, they don't want to be held responsible. They hide the evidence that will wreck their future.
Each later tells their parents a version of the story where one of the other kids actually disappeared LS. The parents my have advised them, in the moment, to do the right thing and report it to the police; fight the drug / alcohol charges. But now that it's done, the parents think that it is safest to stick with 4:30 corner story. It could be very damaging to come clean since hiding a body is a felony. The parents of the boys know in confessing an OD scenario there will be questions about who determined if she was dead or not. And none of the Spierer's pleas absolve anyone from answering these kinds of questions. The parents may not be clear how involved their own kid is with the finger pointing.