This makes perfect sense to me. Kate remembered the conversation with Madeleine because it took place during the last few hours they spent in each others' company, and because she was under scrutiny in police and other interviews. She would have been going through all the events of the holiday in her mind and trying to make some kind of sense of them.
There would have been much less reason ever to recall that conversation otherwise.
It would 'make perfect sense' if Kate remembered that conversation she claims to have had with Madeleine because she was 'under scrutiny' in police and other interviews,, and she was going through all events of the holiday in her mind and trying to make some kind of sense of them
That's not what happened though
She sat down at the table and almost immediately related that conversation with her friends
While she was doing so, according to her version of events, Madeleine was safely tucked up in bed
... No duress ... no stress ... no scrutiny ... no reason to be going through the event in her mind
She brought up the subject voluntarily and without prompting ... the subject she claims would never have entered her head at all if Madeleine had not been 'abducted'