Well I'm going to take a wild guess and say that if you find a desktop with Microsoft OS you're going to find it easier to download the new OS to your 16 gig usb. Maybe the library would let you do it. I would expect Apple to have a no-go block in there to make sure no one tries to load the Microsoft OS on to a Mac (which by the way, a lot of this stuff can be done, by those who have the knowing.) It's been nearly twenty years but I seem to remember I had a lot of difficulty transferring files from a Mac to a non-mac. It is true they have gotten friendlier to that in recent years, but the OS may be a step they don't want to take.
This kind of stuff is out there....
Good luck,
Greg N