Originally posted by bobbotron She's quite a good photographer, she's looking to get rolling with a photo editing suite, I believe she's just using the built in Windows 10 tools at the moment.
Since you have shown her RawTherapee, I assume she shoots RAW at least sometimes. If she's just getting started with PP, she might want to get used to editing jpg's first. In addition to the software mentioned above, I'll mention PhotoFiltre (
www.photofiltre.com). I use v7.2.1. It's my go to editor for jpegs. Free for non-commercial use, and pretty powerful but easy to use. It does layers and masks, can display multiple files at once, and has a broad range of editing capability. It also takes PhotoFiltre compatible plug-ins. Every once in a while a help screen will be in French, but I seldom use them.
For a step (really several steps) up in capability I use Gimp 2.8. Still free (no usage restrictions). My version doesn't do RAW, but I think I read a future version will. Great documentation, including e-magazines, and an active user base. Still seems simpler to me than RawTherapee.
I have heard good things about FastStone as
jlstrawman mentioned. His post reminds me that I want to try it. But I've been using PhotoFiltre for years, so if my workflow ain't broke, why try to fix it?