If I remember correctly, it is with her wife that you get the code, in a kind of quest or puzzle.
Although I honestly don't remember well, I haven't played for a while and I only did it like twice.
You are correct. You can get the code by talking with Lin and then a note will appear in the kitchen.
No note appears for me :(In the guide the "asking Lin for help" step isn't crossed out after I asked her for help... I just guessed the goddamn codeBut it seems I can't get the flag for having cryptic noteIt says I get a note saying garden, midnight but I can never choose any cryptic note options
I appologise for the lack of clarity, the note related to the suitcase requires you to ask Lin about the suitcase and it will appear in the kitchen after that.