I simply choose not to believe SS that Kiely was planning to stay overnight. She seems like an honest, dependable kid that her mother trusted. She told her mother she was coming home, she always came home before, so I am disregarding what SS and ML say about whether she planned to drive home or stay overnight, and believing her mother.
I personally do not get the impression that SS and ML are being honest about the circumstances that night. I also don’t know that I believe she was heavily intoxicated. The first statement from SS was that Kiely wasn’t in the right mindset to be driving, which made me think she was upset, not fall down drunk.
I believe the girls probably had a falling out and parted ways with Kiely very upset and possibly a little bit drunk. ML claims she accompanied Kiely to the party but was only there 10 minutes? It doesn’t make sense. I think these two know more than they are saying.