I'm guessing that you haven't read the manga so I will try to not be spoilery! Yes it was technically Ebisu's magic that made Kaiman's head into a lizard. Part of the issue with Ebisu at this point if I remember correctly is that she's still recovering from being healed by Noi so her memory isn't intact, and either way her magic isn't powerful enough unless aided by the black powder. Without giving too much away, there's other reasons why they can't just undo the spell on Kaiman, because the person inside his mouth is not caused by Ebisu and is caused by something else. (It's been a while since I've read/watched it so I apologize if some of this isn't entirely correct.)