RORY: But a play is not a lie?
LANE: Well it’s far away from the truth that it might work but close enough to the truth that I think I can negotiate a Purgatory stint if forced to.
In Roman Catholic theology, Purgatory is an after-life state where souls are purified in order to make them holy enough to enter Heaven. A soul in Purgatory cannot go to Hell, and is guaranteed to to be admitted to Heaven at some point.
As a Seventh Day Adventist, Lane isn’t saying that she believes in Purgatory, but is using the concept to describe a state where her mother will chastise and punish her for a certain period, yet forgive her at a future date when she thinks Lane has suffered enough.