Lilli lived with her grandfather, a cattle farmer, until his death. She was then placed in the Hull House Orphanage in Orloo, Ontario. She was taught under strict discipline to obey orders and to learn to accept that some things are and she had no control over them.
It was there that it was discovered she had the ability to will herself into an intangible state by the headmistress, Mrs. DeLaSalle. Lilli was allegedly adopted by "The Smiths" but was, in fact, taken by Department H's Youth Acceleration Division's Coordinator Proctor. When she arrived at Department H, she was experimented on, tested, tattooed with a bar code and fitted for a costume to be a part of Alpha Flight.
However, Lilli was slightly rebellious, wanting to return to Hull House and see her friend Claire. She attempted to run away multiple times. In her first attempted she encountered Diamond Lil who thought she recognized Lilli. She also bumped into Puck but he was unable to help her escape.
When the new chief of operations at Department H, Mr Gentry saw to it that Lilli was given free reign through the complex and moved into the Alpha Wing, where she bumped into Flex. The two have become fast friends with a growing attaction. Lilli's first mission with Alpha Flight, under her guise of Ghost Girl, was against the third Weapon X. Since that time, she became a full-fledged member of the new Beta Flight
Powers & Abilities
Ghost Girl possesses the ability to "phase" or literally pass through solid matter by passing her atoms through the spaces between the atoms of the object through which she is moving, she can also make other matter intangible by touching it.
Being intangible she becomes invulnerable to physical attacks. It's unknown if she has the skill with phasing as Shadowcat does. Her powers were never explained; it may be assumed she uses the same process Shadowcat does.
She can also use her intangible body to create gateways through solid objects for others to use. She has created pathways for Puck and Flex to pass through her, and doing so tickles her.