Intimidate Garl for her release (45% Speech required).
Quietly kill the two guards at the rear of the building and pick the lock on Tandi’s cell.
A male character with a Luck stat of 9 and wearing leather armor or using a Stealth Boy can be mistaken by the raiders for Garl’s father, whom he killed to take control of the Khans (50% chance). With at least 6 Intelligence and a Charisma or Speech check, the Vault Dweller can bluff Garl with this ruse and secure Tandi’s release.