Daisy dated Dexter Stubbs while attending university. Along with Dexter and her family, she went on a trip to Australia. The night before Flight 815 left, she and Dexter got in a fight because he'd lied to her about his whole life. It is unknown whether she ended up getting on the plane.
On the Island
Dexter had a hallucination of Daisy and his doppelganger which turned out to actually be Boone and Shannon.