What if they could retcon Zelena's past?

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I think it's obvious that Zelena is "Regina's secret sister we didn't know about," a character they invented for the second half of season three. Seriously, when Rumple made a deal with Cora about her firstborn, didn't he know about Cora's long-lost daughter?

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Anyway, if they could change Zelena's past, how would they do it? I can think of two possibilities:

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1) She's Cora and Rumple's daughter, but because Cora rejected him, he couldn't see beyond the fact that she was pregnant with his child. Cora hid the pregnancy because she didn't want Zelena to take her away from royalty, and ultimately, the green tornado took her. This would explain why Zelena's powers come from being the daughter of the Dark One and a witch (Cora). I think this would maintain the sisterly rivalry with Regina and her reasons for time travel (to reunite Cora and Rumple).

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2) Zelena's adoptive parents are her biological parents; she's born with great powers; the timeline remains virtually unchanged; and Zelena's resentment toward Regina is simply a rivalry between classmates. However, I think the reasons for time travel would be completely lost.

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Can you think of anything else?