I think there's two problems with her. One of which is she's way too slow, which is inconsistent with her portrayal in the Clone Wars. She's is capable of dealing a lot of damage and has a cool skillset but she almost never moves during the course of a match. The other problem is that she has a strong health steal, which makes her aoe dispel redundant. I think that giving her something like "gains 30% turn meter everytime she dispels" as well as giving her a dispel on her basic would greatly help her out.
Also, I'm curious why you think Ahsoka should count as Nightsister? Other than in one of the last episodes of the Clone Wars when Assaj helps her out I don't really see the connection. Why the devs gave Ahsoka Nightsister synergy in her leader ability is something that baffles me..