Her half sister, Hughes, also has memories of a Korean orphanage but recalls little of her biological mother or what happened to her. In 1976 she was also adopted by an American family, growing up in New York state, about 300 miles (480km) from her sister.
Earlier this year, OBrien was hired at a hospital in Sarasota, Florida, working as a nursing assistant on the fourth floor. Three months later, Hughes was hired to work on the same floor.
The two women worked the same 7am-7.30pm shift and struck up a friendship quickly.