I think it’s about the EQ. It would be too much of a link to the hearts she collects! It doesn’t have to be the EQ’s heart that is meant, but maybe of someone who’s responsible for her becoming like this (and I don’t mean Snow xD)
I don't know if it's in this episode or in 18/19 or something but they have an episode about Regina where her mother appears. http://www.tvline.com/2012/01/once-upon-a-time-barbara-hershey-evil-queen-mother/ I think it may well be about how her influence turned the EQ the way she is.
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