Lilly was always crazy. Played through Episode 1 and the first time you meet her, she's trying to kick you and the kids back into the middle of the zombie apocalypse. In fact, the first time she opens her mouth starts an argument with Carley where Carley is trying to keep you alive while Lilly is trying to throw you out into the jaws of death.
The difference is that in the first argument Lilly didn't have the gun, Carley did. In the second argument, Carley didn't have the gun, Lilly did. Lilly was always a poisonous coward and a monster who only wanted people as long as they were useful.
And she never once came up with a good plan until the beginning of Episode 3 (which she screwed up anyway by shooting the bandit you had already negotiated with). She was always telling people what to do when things were calm and then she'd break down and hide when crap hit the fan.
Seriously, Kenny is a friggin' superstar in hindsight. Total douche sometimes, yeah, but he never wanted power or tried to keep it, he was just a natural leader.