He doesn't technically "owe" her, but she went out of her way to save him, she could have just used the idol on herself. Maybe she was showing off a move for later on, but he was definitely going home if she doesn't intervene. Maybe the person who wasn't originally aligned with you and went out of their way to give you an idol to survive a tribal might be a good ally going forward.
If he just gave her a hint she was going home, she stays, Dan goes and is Dean worse off? Didn't see him being really aligned with Dan. IT's probably a good idea to keep players around who will work with you, the game changes quickly.