I figured it out. If you go to this location in your computer:
C:\Users\[username]\AppData\Roaming\itch\apps\goodnight-kiss-2\GoodnightKiss2-1.21-pc\game
there's a file called victoria.rpy. The error is because line 236 is supposed to say quest_items, which is why quest_item is not defined. If you download a python editor like Atom for example you can edit that line to say quest_items instead of quest_item. Just right-click in the file and select 'Open with Atom' and go to line 236.
P.S. The scene was underwhelming so if you don't want to go through all this effort, you won't be missing out on much.