User blog comment:Jkphantom9/Volume 3 Episode 6 Preview/@comment-4010415-20151210011937/@comment-26397825-20151210013356

Ruby did interfere when Cinder was infiltrating the CCT though. Sure, she got away with it, but Ironwood just just a step behind Ruby. If she'd been delayed even a few more seconds, Cinder possibly would have been caught by Ironwood, which would put a major kink in their plans.

It's a grudge thing, really. "You almost got us caught, and you've been meddling with our plans. Well, we're going to take you out so you stop."