I can imagine Alison thinking of the happy, normal, peaceful wedding she thought she was going to have at the start of the book, before BPC turned up, and desperately wanting to believe that it's still possible for her and Ewen to have that

That makes a lot of sense of something that always confused me. But it reminds me of my early reaction to covid - I got rather rules-lawyery, and I think it was my brain trying to assert normality. Silly brain.