The Mods folder has to be in the user folder that the game sees:
https://sims4.crinrict.com/eng/2018/07/how-to-find-your-user-folder/
Some mod managers can help with seeing what a mod is before deleting. Personally, when I'm wanting to delete some custom content (furniture, building items, hair, clothes, makeup -- anything that is in a catalog), I use Sims 4 Studio because it's easy to see exactly what I'm deleting.
Otherwise, my advice is for her to just go through the mods and delete everything that's listed broken in Previously Broken mods and CC and Broken & Updated Mods & CC (just for a quick start), and then everything she's not actually using but downloaded in case she might someday. Another option is just to delete and start over, downloading only what she's in need of at the time, not stuff she might want later.