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.
I also think this is the episode where we learn what Snow White did to make the Evil Queen angry, although I read an episode summary yesterday (don't remember if it was for this episode or a different one), where it said that Regina was given a choice: to choose between true love or a loveless marriage with the king, and the description hinted that maybe her mother wanted her to choose the marriage with the king, over true love.
Because wealth = power, and True love doesn't = power. Which, if Regina's mother is the one responsible for the loveless marriage and not Snow White, Regina has “mommy issues;” not annoying “step-daughter issues.”