She doesn't cause trouble, she's always home on time and she's shown herself to be a very responsible young lady. I let her do as she pleases most of the time. Last week Chrissy didn't come home. I've asked around, and nobody's seen or heard from her.”— Rebecca Royce
Here you will encounter two raiders. One in front of the shack and another inside. High Speech will enable you to free Chrissy without firing a bullet; alternatively, you can gun the raiders down. Be warned though, as the door to the room holding Chrissy is trapped, while one of the raiders, Phil, holds a key to it. High Sneak and Lockpick skills make the way around the shack to back door without that key and dialogue with Phil.
After you free Chrissy, talk to her in her mother's tent.
As a reward, you'll get a red keycard for the Vault 15 elevator, and you'll be able to talk to Zeke, the "leader" of the squatters.