In order for Zelena to enact the curse she HAD to sacrifice the heart of someone she loved. This storyline is not yet revealed.
Zelena, we now know, wants a second chance. It could be that the second chance is to bring back the one she sacrificed his/her heart for the curse to take place.
Zelena is emotionally unstable, angry, spiteful, filled with blind jealousy on how her life turned out. Zelena’s obsessive behaviour, for me, points to a desperation to reverse her rash and reckless decision to sacrifice a beloved heart, a decision made in a furious outburst that she regrets?
Could be a lover, or perhaps an unthinkably horrible mistake, a child she loved? Hence her fixation with Snowing’s baby. This unborn child definitely is the key foundation to this unfolding storyline, perhaps the bold storyline A & E spoke about.
Be who you are, and say what you feel, because those who mind don't matter, and those who matter don't mind. Dr. Seuss