I think what I meant to say that with Sabrina, she was a villain in her time with the Rockets, so what I'm going for here, is a captured moment of time and I'm dwelling on her time as a Rocket. Not after (particularly since I don't have access for future offerings in a real way), that should clear up some things.
I think with Sabrina, it wouldn't be hard to turn her back because she had quite the rush as a Rocket, that emotional release she seeks, is the power in the battle and the temptation of being "bad" and the power angle is the most obvious. Check her performance at Silph with the tri bird and then compare her before that to see the range she possesses.
Although yes, with Giovanni out of the way, her reasons quite dampened and the edge went away and then comes the suppression training that makes Sabrina notorious. But that doesn't mean that edge is forever buried. I'm just saying the temptation can exist. Thus to me, she can be a villain more easily than others, hence my wording, in that she's more likely to show more villainous traits than others or more easily.
Plus, we shouldn't forget her feared image as a psychic Gym Leader should we? No doubt Sabrina's feared image would carry there as well. Although that big tour at the beginning (middle, end?) at Johto, obviously she carried that image as far she could, to give her an edge in battle.
And I think the head Rockets' role in Yellow was more self preservation and "what good is a world destroyed" kind of logic. Although the time with Blue might have changed her priorites, so I'll concede that point.