How to restore individual files from TM backup after clean install?
going to the external drive containing the TM backup with Finder, all folders within her "old" user-folder showed a small red stop-sign, which I learned is an issue with permissions. I wasn't able to restore manually.
  


This is probably the easiest way to go.  

You can fix the "red stop-sign" issue by opening Terminal and entering: 

sudo diskutil disableOwnership /Volumes/[Your TM Drive].

You'll then be able to copy the files over manually, without having to worry about permissions.