Eileen Corcoran was the sister of Bobby Corcoran.
Orphaned at a young age, Eileen took care of her younger brother Bobby, and eventually married Jimmy Gibson, a dock worker. He was eventually killed, supposedly by one of Giuseppe Mariposa's men, and Eileen was left with a young daughter, Caitlin.
Although she looked after her brother, this did not stop her becoming lovers with his friend Sonny Corleone in the mean time. To keep her family afloat, she ran a bakery on Eleventh.
When Bobby was killed in 1934, Eileen was left to raise her child alone.