How about donating to some opensource project like Gimp or Krita, so that everyone benefits, not just Windows users?
Because the parent apparently doesn't like those as much as Gimp / Krita etc? Open source is a noble goal, but not equal to worth donations / money.
Or the parent doesn't know open-source alternatives exist. It doesn't hurt to remind about them, seeing as their development would benefit more people in the long run.
I would donate to GIMP if they started caring about UI.
People who start with GIMP prefer its UI over Photoshop's. It's a matter of getting used to it, really. Or, failing that, "donate" to Adobe to get your ideal UI.
Maybe because the parent has benefited from Paint.NET and it is logical to support them?