He was taking a huge chance trusting that she was actually Jess. She could just as easily be a demon, and actually a demon using Jess' likeness to get to him was far more likely. But if it was her, if she had been yanked out of heaven and drop kicked back on earth, she needed him to be as much like she knew him as he could manage. She sure as hell didn't need him splashing holy water in her face, or shooting her full of rock salt.
"Sit down, Jess," he prompted, and pointed to the booth. He sat across from her. "You remember when Dean showed up, and said Dad was on a hunting trip? I went with him, and when I came home..." Sam shook his head. He wanted to tell her she was gone, play it like he didn't know where she'd been the last five years. "You were dead, Jess. You've been in heaven, and I don't know why you're back."