Why did Esther want Ishmael to think of her as his sister?

Esther wanted Ishmael to trust her.... to think of her as family. She wanted him to open up.

“Think of me as your family, your sister.”

“But I didn’t have a sister,” I replied.

“Well, now you do,” she said. “You see, this is the beauty of starting a new family. You can have different kinds of family members.” She looked at me directly, waiting for me to say something.