Board Thread:Speculation House/@comment-27276671-20160214220907/@comment-69.60.245.202-20160715143340

Maybe but in the last episode of volume 3 the Dragon Grimm noticeably calmed down when Cinder spoke to it, also during her fight with Pyrrha it rammed the tower in an attempt to help her.

This shows that she either has the ability to control the Grimm or at the very least has some kind of kinship with them.

More evidence is in how she initially stole The Fall Maiden powers, with that insect like Grimm coming out of the glove.