Sydney should have known what Barry had in mind when he called her out of the shop for them to talk. She should have read his mind first and found out about his evil thoughts before ever agreeing to leave the shop with him.
However, what was she really thinking was going to happen when she agreed to leave the coffee shop and talk with him outside in the first place? That they were going to act casually and just have a quiet conversation concerning whatever it was that he wanted them to talk about?
She only decided to do him the favor since the both of them weren't supposed to be on talking terms. But then he had to ruin it by showing how ungrateful he was by asking about the same kid he didn't want to be a part of his life, as if he wanted it now.