Interesting story below about a young woman who confessed to killing her friend after police saw what looked like the murder weapon --- her belt --- in a Facebook photo she posted of the two of them. I post this, in part, because it demonstrates that murderous resentment or anger can lurk beneath the surface of friendships between attractive 19- and 20-year-old females, something some here try to discount.
http://www.cnn.com/2018/01/18/world/canada-murder-belt-facebook-photo-trnd/index.html
That's not really why I discount it; obviously, if you google around enough, you're going to find a case that fits the facts of your chosen scenario (which would be true of pretty much any crime).
The reason I discount it is because:
1) It does tend to be very rare, as Skigirl said.
2) The rest of the facts of the case don't fit. In spontaneous rage killings, especially ones involving college students with no criminal history, it's usually very obvious they committed the crime, and their stories are all over the place. Take a look, for instance, at the Blaze Bernstein case:
https://www.websleuths.com/forums/s...ernstein-19-Lake-Forest-2-Jan-2018-7-*Arrest*
That's a case where one 19-20 year old killed another, apparently in spontaneous rage. He tried to cover it up. What happened? Something like this:
Perp: I left him in the park at 11PM and never saw him again.
Cops: Your phone records say you went back to the park at 4AM. Why did you do that?
Perp: Uh, I got worried and went looking for him?
Cops: Where did you go in the meantime?
Perp: My girlfriend's house.
Cops: What's her name? Where does she live?
Perp: Uh, I don't know either of those answers...
Cops: OK. Why are your hands all scratched up?
Perp: Uh, I'm in a fight club.
Cops: Why is there dirt under your nails?
Perp: Uh... I fell in a mud puddle.
In other words, they didn't plan it, they panic after the fact, their story doesn't make any sense, and it becomes immediately obvious they're lying. That guy got arrested in less than 2 weeks. In the case you cited, the girl actually confessed when confronted with evidence.
With KR, there's a bit of circumstantial evidence that seems suspicious
only because it happened the night Faith died. Had that not been the case, it would totally make sense within the context of a rowdy night amongst college undergrads.