In 1977 Eloise Hawking shot her son, Daniel. On him was a notebook, which she would give to him years later. Written in the notebook, we could presume, is everything that happened to everyone on the Island, including how Jack said they got back.
After her words to Penny in the hospital, "for once, after a very long time, I don't know what's going to happen next". She had Daniel's book for the whole time.
She read the part about Jack saying she would later tell them they need to recreate the flight and it was their destiny to return and all. They never actually had to recreate the flight to return, but since Jack told Daniel that, it was put in his book and later went to Eloise, where she believed it was her destiny to follow the book's "guidelines" and make sure each character eventually made it back to the Island.
After they returned, and history looped itself, ending with Jack telling Daniel all this (which we only saw part of), there was no more in the book to be read. Eloise was then on her own, and had completed her "most important part of her life".
What do you guys think?