I have heard this stated before by some long-term posters I admire. And I respect your point which I can conceive could be true. But Ive a few concerns which keep me from embracing that idea as an absolute. I dont doubt that Patsy physically wrote the RN. However, given the housekeeper LW claimed the verbiage in the RN reflected both of the adult Rs speech, I cant dismiss that JR had a hand in directing some of the material in it....
As another poster has noted, you seem to be talking about LHP rather than LW. I looked at the first chapter of LHP's book. (It's
supposed to be hers, anyway.) I don't remember seeing anything about John's language. It did say that Patsy used hence frequently and also mentioned that she was particular about putting the accent aigu in JonBenet's name.
I looked at the ransom note and it might be that the acute accent is missing in attache. (I think we're just seeing a forward tick on the downstroke of the y in the line above. Other y's in the RN exhibit that.) I looked at Forensic Linguistics by Gerald McMenamin to see what he decided the ransom note and Patsy's five exemplars exhibit vis-a-vis attache. If I'm interpreting his "vertical score format" correctly, he thinks that both the RN and Patsy (consistently) omit the accent in that word.
It seems a little odd to me that a French-accent fan like Patsy would omit the accent in her exemplars. I would put it in and I'm no Francophile. (I can't see the actual exemplars for that word so I'm going by what the word-processed text indicates.)
John, on the other hand, puts an accent on attache in at least one of his exemplars. At least, the book says that John uses the "longer form" of attache in his second exemplar. That makes it into John's stylemarker list because only forms that differ from the ransom note are allowed into Patsy's and John's stylemarkers. (Don't get me started.)