Rescue Sinthia: If one spends the night at the Crash House, Marcelles will ask them to Save Sinthia from a crazed raider in the room next to theirs. Once completed, Sinthia will now be available for "services" (including, but not limited to, the Tell me about feature).
When asking Sinthia to "tell me about" various words familiar to her profession, she feigns ignorance.
If the Vault Dweller used her "service" before, once in a while if the player character returns to Junktown and walks past Crash-House Inn, there will be a text that says they "feel a sudden urge to visit Sinthia again."
Playing as a female, Sinthia will not be available for "service," but if they have a higher Luck, she will allow it once when talking to her about her boss directly after rescuing her. If one fails to persuade her, she will instead quote both of you being women.