I found it very consistent, actually.
Starcraft 1 starts out with Sarah Kerrigan as a principled do-gooder heroine who ends up in love with Jim Raynor. Then, she gets infested.
This visibly alters as what she is. She manipulates everybody and betrays them, sometimes more than once. She skillfully uses what everybody thought Sarah Kerrigan to be to pretend she was still that person, and then she turns out to be an evil monster that ends up on top by screwing everybody over.
While she is vastly more powerful than the average infested Terran, all you have to do in SC1 is infest a Command Center, produce an Infested Terran and repeatedly click on him. An infested Terran is a Zerg puppet, and Sarah Kerrigan was the same. She was made by the Overmind to escape his overriding directive by Amon, but though she gained the independence the Overmind sought of her, she still ended up tainted and twisted, no longer the person she once was.
Then, Raynor cleansed her using the artifact, and she honestly didn’t remember most of what she did. This has to be true because when she comes back to the Leviathan, she clearly only remembers tiny bits, though at that point she has no incentive to hide what she knew. For example, she remembers Izsha, but while she has rage at Abathur, she doesn’t even remember why, (it was because it was he who made her from human to QoB.) She has to re-learn things as basic as the Brood Mothers being her intermediaries with the Swarm. Keep in mind she is the one that created Brood Mothers to begin with; the Overmind used Cerebrates.
When Kerrigan becomes QoB the second time, she is no longer being influenced by Amon and while she looks similar, she is vastly greater in power and independence. She remarks on both, saying everything has changed and that never again will the Zerg be pawns of other races.
She then inculcates human values into the Zerg. Abathur is relieved when she tells him no more experimentation on humans. Before this, she wanted him to put failed experiments out of their misery, which he initially didn’t understand becuase it didn’t impact experiment success or failure. Zagara starts out wanting to take the Swarm from her, but when Kerri is critically injured in her fight with Narud, Zagara saves her, and at this point you can see she follows Kerri out of loyalty and not of fear.
Keep in mind this is only true of QoB past cleansing, not of the original QoB. Even after she believed Raynor was now dead, she still behaved this way.
And of course, there’s the fact that after Raynor cleansed her, even after she became QoB again, she genuinely cares about human life, valuing the same in Valerian and agreeing to hold back the Swarm during the invasion of Korhal to avoid civilian casualties. This is what convinces Raynor that she’s his Sarah again, not what she was as QoB in SC1. This is because the QoB in SC1 was a treacherous morally-dead expletive that would never behave this way,.