Same thought as hjbau, SW tells Cora, Cora confronts Regina and tells her to forget it, Regina considers running away with the stable boy (maybe that is what SW tells), and Cora stops them by killing Regina’s true love (or turning him into a toad) and ruining her happiness, which Regina perceives being SW’s fault. I don’t know, somewhere along the way, the thought occurred to me that perhaps she kills her mother in revenge, but then she loses her mother and her lover and vengeance seldom brings true satisfaction, and when she realizes what she has done she blames it on SW, who if she hadn’t told Regina’s secret to begin with, she perceives none of this would have happened and she would be living happily ever after having run away with her true love. Who knows, maybe her lover is the apple tree. We know she brought the tree with her to the palace.
I THINK this is one of the best and most accurate theories…. I heard SNOW is a young child when this happens ( about 8-10 years younger) ANY ONE WHO HAS RAISED LITTLE GIRLS / OR HAD A YOUNGER SISTER KNOWS you can not tell girls anything… THEY BLAB.