Hmm. Well, since we already know that Cora is going to have her backstory revealed in this episode, here’s my theory.
The miller’s daughter story plays out pretty much like we know it, with Cora needing to spin straw in to gold for the King (who in my opinion is George) because the kingdom is in financial trouble, she can’t do it, she gets help from Rumpelstiltskin etc. She marries the king, and for now she doesn’t have to spin gold anymore because the kingdom is doing well. Cora enjoys being Queen and the power that comes with it. She even falls in love with the king. Then she finds out she’s expecting and Rumple wants to take her child, but she desperately finds a loophole in his deal and gets to keep her on a technicality, perhaps involving her returning the magic spinning wheel. Then the kingdom is in trouble again, and the king wants Cora to spin more gold, but alas she can’t anymore. The king is angry at Cora for lying to him, and since he never loved her and only married her for her gold-spinning ability, he tosses her out of his castle and tells everyone in the kingdom that their queen is dead so that he can remarry. (This is my explanation of why Cora is so insistent that love is weakness. She loved the king, but he betrayed her, and her love of her daughter made her get kicked out of the palace.) So, poor Cora is alone and pregnant when a kind man of good fortune pities her and comes to her rescue. He’s no king, but Cora marries him because she has nowhere else to go. She gives birth to a daughter, but knows the king will never recognize her as his own, so she becomes determined for her daughter to become queen, as is her right by birth.