I think of the events this way: John appears to have been a womanizer during his first marriage. On that topic Vanity Fair says this: "According to police reports, his former wife, Lucinda, said it was a romantic liaison with a co-worker that was the last straw for her. Although [Jim] Marino and Ramsey caroused 'and whored around together,' Marino says Ramsey was notably discreet." I'm unclear as to whether the "whoring around" was just during the separation period, but his first wife clearly thought he had affairs plural during their marriage."
It seems possible that Patsy suspected John was cheating on her and he that may have done something besides visiting his plane Christmas day. Perhaps she thought he was disappointed that her cancer had gone into remission and he had been looking forward to being rid of her without the expense of divorce. If his eye then wandered at the party, she might have been in a barely controlled rage when they got home. She didn't go to bed. What was she doing? Packing? If so, that could have made her even angrier.
Then she lashes out in rage at JonBenet and she's in a major pickle. In her position, I would assume that John would figure it out and turn on me. Colorado's not a community property state so when he divorces her, she's only going to get what a judge deems suitable, and that might not be much for someone who killed her child. In her position, if I hated my spouse, I might try to frame him or at least put him in the same jeopardy as me.
So I speculate that she put the ransom note on the floor to induce John to pick it up and get his fingerprints on it.
I have a mismatched and misplaced " in the above. The sentence "I'm unclear as to whether the 'whoring around' was just during the separation period, but his first wife clearly thought he had affairs plural during their marriage" is my own, not Vanity Fair's. Just to be clear.