I was pretty sure that Ashleigh Ball was voicing all of them (RD, Spitfire, Lightning Dust) and basically ended up talking to herself the whole episode Spitfire even channeled a bit of AJ at one point. IMDB disagrees with me though, I guess they were all just similar voices.

If there was any doubt before in the first place, RD is awesome again after the previous two episodes. I felt she needed them, and there they are