This is a combination of Kate's mom calling her "Katie" right before she threatens to sic the FBI on her and the fact that I really like Kate and Juliet interaction.
Juliet doesn't call her Katie. Never again after the first time when she walks up behind the
younger woman on the beach, wraps her arms around Kate's waist and says "good morning
Katie," in a joking and affectionate tone and that somehow causes Kate to freeze, slide out of
Juliet's arms and not talk to her for three and a half days. She isn't sure why the pet name is not
allowed but she guesses that it has something to do with Kate's mother. So she doesn't broach
the subject with her again. They don't really need pet names anyway.