Board Thread:General Discussion/@comment-5047068-20141123201355/@comment-25393251-20150120002642

More than likely her semblance is teleportation. The train scene in Volume 2 showed that dust can be used to affect semblances, so it logically makes sense that there was some kind of 'glass dust' (Highly possible, since Cinder uses a similar dust) to affect her teleportation to leave behind a glass illusion.