She could be filling the hole that rejection has left in her heart. If you look back she tried to force Hanzel/Gretel and Owen in being their mother. They all rejected her and she was unable to “force” them to love her. She in turn lashes out to make their life miserable. She does the same with Snow. She activates the curse and gets bored in a sense. So she wants a child and adopts one. Henry in turn rejects her over and over again.
I think all the rejection would make anyone miserable and evil. She has been rejected her entire life. Also, you would think Cora’s last thought would begin filling the hole a little bit. However, the damage has been done.
I wonder since this is the rescue Henry, child season if they will dwell on this at all.