She surrounded herself tightly with the wall of her heart
No one has entered
She is afraid of being hurt
That person gave her happiness. When the wall of her heart slowly collapsed, he abandoned her and left. She swore she would never love anyone again because of the pain of being tortured. She didn't want to go through it a second time.
Her layers of protection would still be penetrated by sunlight, all the way to her heart.
She will have a good life, even if there is no one in the world who cares about her. She will still live well and face every pain with a smile.