From The Grey House:
Anthony was standing with his arms crossed, angry. He did not trust Natalia but didn’t seem to know why. Vincent didn’t think it necessary to tell Anthony about their first meeting and was more comfortable having one of his people suspicious about the human. His emotions were too tied up and confused when it came to Natalia. Joseph, usually suspicious of everyone, was uncharacteristically silent about his boss’ new woman; therefore, he let Anthony be suspicious.
“Why go after her Vincent? She’s a Slayer.” Anthony didn’t bother hiding his emotions.
“No, she’s not.” There was dark humor in Rebecca’s voice. “You should see what she did to the one we caught.”