I love it for either sex, but I do prefer it for a girl, as a middle name.
Quinn and Lilah don't sound mismatched at all.
Mariel Quinn is dashing.
Random
Quinn ideas:
Quinn AmeliaQuinn Eldora (a real name, I promise)
Quinn FeliciaQuinn OpheliaQuinn BeatrixQuinn IantheQuinn JulianneQuinn PandoraQuinn PenelopeQuinn DesdemonaQuinn Teratia (ter-AY-shah, again a real name, I swear :)
Quinn AmbrosiaQuinn WinifredQuinn EleanoraQuinn AureliaQuinn StephaniaQuinn Melanthe
Quinn UrsulaQuinn RebeccaQuinn HarrietQuinn VioricaQuinn Alexina
Array
"That was the thing about aliens that no one ever really expected. They're a bit dull."
A revolution without dancing is a revolution not worth having.