what a weird thing to say to someone... "bad faith" for not implementing something to YOUR wants...
As far as I'm aware (although I'm a programmer as well, I don't program games) its just a matter of exporting to linux, if that's not the case I apologize, but usually with game engines like godot or unity (with unity I'm sure this is the case) all you have to do is click one button and ta da linux version... You did not think she had to code the same thing twice right? She had to put some checks about the os in the window location parts, since that is using window's own api, but again as far as I'm concerned, the rest of the code should be as easy as to click one button to compile it to other platform :)
Out of all the kinds of "games" one could make, this desktop pet would probably require the most custom code to work on Linux. How many different desktop environments, windows managers, etc are there to support? What a nightmare prospect it would be to port this to linux. Yikes.
Bravo to Rachel for getting it working with Windows
If you check the video she made about it, it is clear that it pulls specific Windows DLL into the running code to access extra window features that are needed to make it run. It won't natively run under Linux.
So in this case it's not just about exporting to another platform. It's using features not supported by Godot itself. It even explicitly needs the C# version to use the PInvoke functionality.