When Paul decide to talk to Cassie about Mitchell he explain to us the reason in this passage, he described her as “not only beautiful, she was tough, smart, and just a bit cocky” we can infer that she could give him a good advice on how he needs to handle the situation, he also says that she was “pretty much like a mother hen when it came to him” and he she would “take his part” so she will be supportive to him. The answer is He knows that she will support him and give him good advice.
