Liv's smile crumbled as soon as Uriel's skin touched hers because that was all she needed to gain access to his memories. She knew everything about his harsh upbringing, his feelings, his friends and more importantly, she knew Uriel had found out she was the skinwalker.
Actually, Uriel had suspected her from the minute he saw her. His mystical sense didn't alert him nor did she act in a way that could have been described as suspicious for a girl her age, but when Alan disappeared he had turned to look at her because she yelled. Besides, even if she didn't try to get Charlie and him to fight each other she had tried to push them to break the rules over and over. Not just that, once they found a safe place she started to become anxious, which was contrary to what one would expect from a scared girl.
The confirmation of his theory came when Uriel asked them to go to the watchtower, since it was a senseless idea that came with no benefit at all.