Margot writes to Anne, encouraging her to enjoy her friendship with Peter. It’s very clear that Margot’s not interested in Peter romantically because she says she thinks of him kind of like a younger brother. And since Margot and Peter are the same age, that means she’s not attracted to him at all.
Anne confides in Kitty that she thinks that they may have the makings of a great love in the Secret Annex, but she is not thinking of marrying Peter.
She knows Peter loves her, but she’s not sure if he loves her like a sister or like a girlfriend.
Anne thinks he is handsome now, in addition to being "sweet" and "beautiful." Can we trust her judgment when she thought he was so boring before?
She writes back to Margot, saying she has to wait and see what happens between herself and Peter. If she and Peter decide to "be friends," she will be sure to tell him that Margot is also very fond of him.