It's speculated that Dooku, as a former Master Jedi, was always in control of his emotions and thus never fully taxied to the dark side. Reva does not possess any of this discipline. Dooku was a political idealist who probably thought he could control or at least not be controlled by Sidious. Reva's motive is purely revenge, just like Maul. Again, you would think that this Sith-like goal would have sullied her in some way. Call me crazy.