Initially Dean was Sam's brother in her mind. Okay, so he IS Sam's brother, but now he is Dean. He is his own person, and she cares about him a lot. She doesn't click with him in the same way she bonded with Sam. It's a different kind of closeness, but she would still do anything she could to help him if he needed it. (And boy does he need it sometimes! But I kid!) He is a fun person to be around. She feels relaxed around him and enjoys his company and his teasing. She likes teasing him too. The strip club incident made her uncomfortable but that was mostly because she was already uncomfortable with the body and he pushed her far enough for her to lash out a little which also shows how relaxed she is around him. Otherwise she would have been more dedicated to being polite about it.