The thing I learned about prophecies from Star Wars, Yoda put it perfectly in Revenge of the Sith: A prophecy . . . that misread could have been.
I feel like that’s what happened. Glinda thought that meant Zelena, then maybe Zelena thought after Dorothy’s arrival, it meant Dorothy, and then we all thought probably, it meant Emma taking down the wicked witch because that’s what we expected. But really, what the prophecy meant, was Regina taking down Zelena.
And Snow and Charming even thought when they found Glinda that the white magic that they needed to defeat Zelena was Emma’s magic but of course they didn’t realize at the time, as soon as Regina found Robin Hood and fell in love with him and shared True Love’s kiss with Henry, that Regina was the one who was going to defeat the Wicked Witch.