I had the same problem... I remember having asked her earlier if she lived in the city and being told by her that she lived in Fartman's territory, but I either didn't get the key at that point, or the key was lost at some point as I went along.
Another thing that you should watch out for is when you finally find Harley whatsisname, do all of the other dialogue options before talking to him about Mrs. Maria, or else he'll be stuck in that area and you can no longer advance Apo's quest.
This is the first build that I've played this game, but I like it a lot. I watched someone play through Harvester (1996 horror adventure game) several months ago, and this seems somewhat inspired by it (although, clearly, in a much more lighthearted and comedic sense). Looking forward to seeing where it goes from here, and I'll have to try out the neighbor route next build.
Two criticisms: 1. Scrolling to the right with a multi-monitor setup is awful. You can usually get by when scrolling to the left (at least when the game is full-screened, but on the right you'll often fall off the screen, causing the window to lose focus when you right click, and the game locking up for several seconds at least). Solutions include making the scrolling boundary on the right half of the screen a bit wider, and preferably implementing some manner of borderless windowed mode. Another solution would be allowing for the direction keys to move either the character or the screen, so that the mouse has somewhat less of a burden when it comes to navigating the game.
2. The game never really makes its way back to original graphics quality after pressing 1 or 2 for black & white mode, "cartoon mode" or whatever else. I hit them by accident when trying to quickly move through dialogue options (figured I'd see if it worked) after getting beaten up by Giulio multiple times... no matter what buttons I pressed (1,2,3 various other buttons on the keyboard) it never found its way back to good-quality graphics. It would be good if those options were more difficult to enable accidentally, either putting them in the options menu or on less "obvious" buttons.