I think it would be great if she just drowned in Water. No magic needed for that. But it would still pay homage to the original Wicked Witch story.
Another thing Z has been going around trying to get all these ingredients Charmings courage Reginas Heart and Rumples brains and now she is after Emmas magic or more accurately as it was said in last ep she needs Emma without her magic right?
So what if what she needed from the other three was not courage, brains and Heart. but for them to be without it? meaning she needs Rumple brainless, Charming David courageless, Regina (well just not to exist) and Emma powerless. This she needs in order for the Alternate Reality to Work, so that neither of them can undoo it ones it is done. If Rumple still had brains in AU he might be able to change it back and so goes for Charming with courage and Emma with magic-
Okay! Im just so bad at explaining this but do you get my meaning?
But somehow maybe Hook and Emma is able to trick Z into thinking Emma is powerless when Z then puts the new curse to effect. Emma still has powers and Emma will therefor be able to somehow undoo the AU. Being the savior, that would seem fitting.