Juliet writes Sophie again and instructs her to burn this letter as well: she's just refused Mark for the last time and she feels free. The morning after Mark's arrival he showed up, tried to fix a wedding date, and asked no questions about Juliet or what she's been doing. When Kit came downstairs Mark was nice to her, but became annoyed by her presence. After Kit went outside, Mark sighed about Juliet's friends saddling her with childcare. He went on to say that Juliet should get Kit a doll and say goodbye before Kit gets too attached. Angry, Juliet whispered at Mark to get out and said she never wanted to see him again.
The fact that Juliet only rejects Mark after he speaks poorly of her friends and of Kit in particular suggests that Juliet is thinking of herself in an increasingly parental way when it comes to Kit, and she won't put up with having this questioned. This suggests that while Juliet may be an independent person, she still needs that extra boost from having someone else depending on her to stand up for what she wants.
Mark tried to argue, but Juliet held firm. She feels now that after a year of marriage, she would've been scared to think for herself. Mark left two hours after their fight and Juliet spent her afternoon eating pie with Amelia. In a postscript, Juliet assures Sophie that this doesn't mean anything about Dawsey.