- Played by Cynthia Watros
Before the crash
- Was in the tail section of the airplane
- Clinical Psychologist (she told this to Sawyer and Ana-Lucia)
- Dropped out of medical school after one year
- Was injured while racing "a cute Ski patrol guy" in Stowe, VT
- Was a patient in Santa Rosa Mental Institute the same time as Hurley
On the island
- Performed triage on Tailenders after the crash
- Lived with the Tailenders in the Arrow station
- Lies to Sawyer about how bad his wound is to motivate him to keep going (she says that she is a psychologist)
- Seems to babble a lot, but this may be the result of stress or the clever use of her psychological training
- Flirted with Hurley in the Swan bunker's laundry room in an effort to distract him from thinking about why she looks familiar to him.
- Told Hurley that he stepped on her foot while he was boarding the plane
- Helped Claire to regain her memories of the Medical Station through what looked like hypnotic regression.
- Helped Hurley to rid himself of his eating habit, only to see a parachute full of food appear on the island.
- Stops Hurley from jumping off a cliff.
Theories
- Libby knows about "the numbers" because she was at the mental hospital with leonard also
- She's interested in Hurley because she knows he's rich.
- May be a compulsive liar
- Could be an other, getting close to Hurley because he has the Oceanic Flight Manifest.