For my SI I kind of focused on the fact that she used to be a slave (and subject to quite a bit of abuse) and did not willingly join the Sith. Arrogant, cynical and ruthless but does not hurt people for fun. As in: "I am willing to blow up a planet to further my goals, unless the objective can be accomplished by less radical means. Destroying planets is expensive, time consuming and is frowned upon in a polite society." Interestingly enough she ended up being LS even though I expected mild to medium DS.