I don`t feel that the book revealed any emotional release which had not been already expressed...........and although the diary was not intended for public view, the act of writing it for her daughter would possibly have served its purpose as "cathartic."
Imo the book was simply a way to reinforce the "abduction" idea to a wider readership and add to the fund.
I agree Carew
I maintain that in psychological terms catharsis is reached by expressing previously withheld or repressed emotions
Kate's book is largely emoted through anger ... an emotion that no-one can claim has been withheld or repressed at all
The emotions that Kate has never expressed are those of guilt and shame
Whether that is because she is repressing those feelings, or because she doesn't actually feel them, we cannot know, but, in any event, they were not expressed in her book
Had she expressed such previously unshown emotions then the book might be viewed as cathartic
She did not, leading me to agree with your view that the motivation for writing it was to reinforce the McCann narrative, and to generate money to cover ever increasing legal fees