Kaeloo and Quack Quack have a very good relationship. Sometimes, Kaeloo acts a lot like a mother to Quack Quack. They rarely ever fight, and they like to do a lot of things together.
Kaeloo admires Quack Quack because he is very talented at everything, as well as polite and kind. She is normally the one who stands up for him when Mr. Cat torments him. She sometimes scolds him if he does something wrong, but this doesn't happen very often. She sometimes appears to favor him over the rest of her friends, such as in "Let's Play Doctors and Nurses" when she tries to take care of Quack Quack, who is perfectly fine, and callously ignores Stumpy, who is seriously sick and needs someone to take care of him. She can also be very strict with him when she believes it is necessary, such as forcing him to choose between giving up yogurt or leaving Smileyland (she later regretted this as he chose to leave). In "Let's Play Truth or Dare", when both of them fell in love with Eugly, Kaeloo decided to let Quack Quack have her since she wanted him to be happy. After Quack Quack creates planet Yogurtland in "Let's Play the Very Special Episode", she expresses disappointment in him for having betrayed her trust. After he destroys Yogurtland, Kaeloo decides to forgive him, but doesn't forget what he did.
Quack Quack is also very nice to Kaeloo and plays games with her even when nobody else wants to. He seldom gets angry at her for anything. In "Let's Play the Very Special Episode", he destroys Planet Yogurtland after seeing how unhappy Kaeloo (and the others) were. A flashback is shown in the same episode which shows that Quack Quack may not be all that obedient. When Kaeloo was putting Quack Quack to bed, he wanted to eat yogurt, but she told him not to since it was his bedtime. After she left the room, Quack Quack pulled out a hidden stash of yogurt and ate it. When Kaeloo came in to check, he pretended to be asleep, and then continued to eat after she left. In "Let's Play Paper Balls", he gets angry at her for suddenly attacking him (which was not her fault, because Stumpy and Mr. Cat were controlling her with magic paper balls at the time).