Negan definitely has a code (all his own) and his actions almost always have a purpose, despite how whimsical they may seem at the time. I think he proved that the day he killed Spencer, and Olivia while waiting for Rick to return home (even if those events haven't taken place yet in this game). Olivia was punishment for Rosita trying to kill him, and Spencer for trying to undermine his leader, which Negan DOES have a respect for Rick, even if he's constantly belittling him. That's just the asshole in him, though I feel like he's a reasonable guy if someones intentions are pure.
I actually really like the angle of her thinking she could do better and is just sort of buying her time to strike out against him. I think it's a very plausible plot that'd be fun to explore! He's smart though, so he makes it as hard as he can for people like that to rise up against him, but he obviously has his weaknesses. Ones she'll have to discover for herself of course ;)