The story Zara told Damien wasn't riveting or heaven-shaking, it was quite ordinary in fact. Still, he could clearly feel from her tone how monumental of an impact Tang Lingzi's presence had on her life.
When she took Zara in, she was in the worst mental state possible. Her mental age didn't match her physical age to begin with due to her growing up in the First Dungeon. Only after she met Damien did she begin to develop.
However, developing emotion and complex thought wasn't always a good thing. As Zara became more aware of her surroundings and the meaning behind the interactions around her, she became scared. She was scared of the world that suddenly turned complicated and her role within it.