I’m finding it hard to believe that she was at the party that entire time. Here's a potential alternative series of events.
Between when KR is seen on surveillance cam in Truckee and ~9, something happens to her.
Three people are with her when that thing happens and they spend the next few hours whipping up a plan.
Two people go with her phone to the party - I'll just refer to them as person A and person B. One person, Person C, is already at the party. The two hand off the phone to Person C.
Person A and Person B leave the party. Person A will hold onto both person A and B's phones for the remainder of the night to allow the phones to ping far away from KR's phone and give them an alibi. Person B will take KR's car and drive it as far away as possible to a predetermined location and hide it there and wait to be picked up by Person A. Person A will send a text to KR's phone sometime during this time period to "prove" that they had their phone with them and had really left the party and that both of them are alive and well and not with KR. Person A then leaves to go pick up person B from the car drop site that they both had agreed on ahead of time. Person A leaves both person A and person B's phone behind at home or wherever they went to after leaving the party, while Person A goes to pick up B from the drop site.
Person C meanwhile, spends the night with KR's phone. Person C will claim they were with KR in KR's car charging phones but never be seen with KR at the party. Person C replies to the messages sent to KR's phone and helps construct a completely divergent timeline to throw off the police. Right before she leaves the party, Person C calls their own phone from KR's phone and then ditches it somewhere. Person C gets in the car with a random group of people and heads home.
No idea where KR's body would fit into all of this but wouldn't be surprised if it is in the car that was ditched and will likely not be found for quite some time as it is in a completely different direction from the search.
Let me know if there are obvious flaws in this theory. It's just that, a theory - because a lot of this doesn't add up to me!