This show and logic do not coexist. In this case, the show has a problem where too many characters have all powerful magic and they need to create random illogical reasons why they can't use their power. Rumpel should be able to kick everyone's ass, but is either apathetic or motivated to not help/actively work for the other side. Regina's magic is now rated below Zelena's because reasons. And we have Emma, who is supposed to have super powerful True Love white magic, but can't because then the story would be over immediately. Logically, if Zelena had just gone about her business, she could have done what she wanted no problems, but there's no story there either. Instead we have all knowing Zelena planning to remove Emma's magic via kiss curse with no explanation of why, if she has this power, she doesn't just roofie Emma's water or something. It's stupid and only used to add drama to Captain Swan.