Board Thread:Episode Discussion/@comment-34633327-20180112214926/@comment-4010415-20180115013716

94.254.138.211 wrote: What if SEWs power only affects maidens when they actively use they powers? . Mayby the reason why Cinder was affected by SEWs power and Raven not was because Cinder was actually using Maiden power at the moment when Raven was not. Note that Cinder gripped her Grimm arm when Ruby used her SEW powers, meaning that what was being affected was the Grimm parts of her.

And there's also what the anon above said - Cinder didn't have her Maiden powers active when Ruby blasted her the first time in Volume 3.