This is just one of my new and somewhat implausible theories, but it would be quite interesting if it were true...
In the Freighter Four flashbacks, we see a woman who is living with or taking care of Daniel Faraday. They did not show us her face for a reason.
I think it's Libby.
We've met Cuckoo for Cocoa Puffs Libby (in Hurley's institution) and Widowed Philanthropist Elizabeth (who gave Desmond her deceased husband's sailboat).
I know, I know...Libby would have been on Flight 815 and then on the island during Daniel's flashback. Or not.
Look, we don't know for sure when the Freighter Four flashbacks occurred in LOST time, and it's possible that Libby had a twin. Off-island, both flashbacks featured brunette versions of her.
Just a thought.