Hello,
I think we may be having a similar problem due to Origin and mac. So apparently Sims 3 is a PC game running through an emulator called cider, which can be found within the program files that Origin downloads in The Sims 3 folder under applications.
Anyway, the problem you're having is the game is creating files under the transgaming folder and is not creating a The Sims 3 folder in Documents like it is supposed to. Instead, it has put EVERYTHING in The Sims 3 folder in applications. Once I clicked through a crap ton of dead paths, I finally found one that gave me all of the folders that were supposed to be in Documents.
To find the folder that should be in Documents but is not, go to Applications and Right Click "The Sims 3" and click view package contents.
From there it is Contents>Resources>Transgaming>C_Drive>Program Files>Electronic Arts>The Sims 3>Game>Bin>%USERPROFILE>My Documents>Electronic Arts>The Sims 3
So you can see from the file path that after transgaming it creates folders that look like they belong in Windows. I added my mod folder here and everything is working beautifully now. I hope this helps you and others!
