I don't really see why she didn't at least try to cooperate with Kate before resorting to violence. Even if she's short on time they have the same ultimate interests, so I would think they could have come up with some sort of plan together...
I've always considered Campari to have a sort of strange cloying sweetness underneath the bitterness, so maybe that's what they're referring to here. It's definitely more bitter than sweet though so for the purposes of a cocktail I'm not sure how important a role the sweetness can play.