The thing is we have not seen a redemption moment from Amara. We infer her purpose is to free her sons, but she did a lot of evil things to get to that point. Rumple acknowledged that and sacrificed himself so you would kind of think Amara would have to do the same.
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“If I had a world of my own, everything would be nonsense. Nothing would be what it is, because everything would be what it isn't. And contrary wise, what is, it wouldn't be. And what it wouldn't be, it would. You see?” -- Lewis Carroll, Alice's Adventures in Wonderland & Through the Looking-Glass