Four hundred years ago, Irene was a kind individual, having undergone political marriage to protect her country and end disputes. She was a firm believer in human-Dragon coexistence, best exemplified by her relationship with the Dragon Belserion, confiding in him her sadness at the mere thought of Dragons eating and mistreating humans, and even creating Dragon Slayer Magic so as to help the coexistence faction win the war, all with his help, all up until his death at Acnologia's hands, which left Irene particularly distraught. She was also extremely maternal, halting her fetus' growth with Magic when she was imprisoned for undergoing dragonization, and sped up the process solely to protect her. During her several hundred years of being a Dragon, Irene became obsessed with returning to her human body, and eventually, after getting it back, becoming a true human again. This obsession turned into insanity and desperation, with her trying to enchant herself onto her yet-still-unborn fetus and failing, which ended with Irene abandoning her newborn infant in Rosemary Village. This marked Irene's complete departure from how she used to be, and from here, she ultimately became the vain, cold-hearted and cruel individual in the present.
The above account of events is later stated to be false by Irene: she could not bear the idea of doing any sort of harm to her smiling infant (whom she loved), and instead opted to leave her, quite gently, in the care of someone else. Irene merely contrived the facade that she heartlessly abandoned her daughter as a means of coping, for when she came face-to-face with Erza many years later (and had her at death's door), she ultimately opted for suicide, still unable to actualize the desire to kill her daughter.