Why does Dearbhla decide to try to find Eliza's husband?

The child Dearbhla raised was an orphan child. She told everyone he was her dead brother's child. However, when Dearbhla lived on the plantation, a woman named, Leena, brought the child to her when he had just been born. His mother was a slave who died giving him birth. His father was the master of the plantation. Leena persuaded Dearbhla to raise the boy.