Sierra's frustration with her obstinate friend only grew the closer they got to their trip up north for those brain scans. Sure, she was a bit apprehensive about the whole thing because she hadn't met the people in question but Nathan trusted them so that was good enough for her.
Besides, she had no doubt he would protect her if any of them did try to pull something weird. He looked out for his own even more than he did random strangers.
She had noticed this the more they hung out. In addition to having his usual emergency supplies he started bringing her things he thought she needed like a scarf, beanie, gloves, and hand warmers after coming out unprepared one day.
He frequently bought her snacks while they were out too in exchange for her steady supply of baked goods. She hadn't asked for them; he simply wanted things to be fair.