Always Prints at 200%

That's strange. In Safari, the scale always reverts back to 100%, no matter what setting is used. AFAICT, the scale setting in Page Setup is retained when the document is saved. Open an untitled document (TextEdit is used for this example), select Page Setup (CMDSHIFTP), set the scale to 100%. click on the Settings: dropdown, and select Save as Default. Your colleague might have to do that for all text and other programs.

The above is correct. Use TextEdit or any other app that has a Page Setup Dialog, set the scale to 100%, then use the Save As Default in the Settings menu.

Another solution is to delete the com.apple.print.PrintingPrefs.plist file in /<home>/Library/Preferences. That will reset any other preferences you have set though.

I looked at all those printing plists, but none of them addressed the Print Setup scaling factor. I surmise that those are buried within each apps plists, so doing the Save as Default thing is probably the best way to solve the issue.

I couldn't find the scale in any of the plists either, but throwing away the com.apple.print.PrintingPrefs.plist reset the scale to 100%. I don't think that the scaling factor is saved on a per-app basis, because of what happens when throwing away the com.apple.print.PrintingPrefs.plist file and also because making a change to scale in TextEdit causes the change to appear in, for example, Safari.

That said, your way is probably the easiest and the safest.

Thanks for the follow-up. I don't have the issue, so deleting the plist won't change anything. Let's see what the OP tries.