I am not entirely clear that this whole thread is necessary.
If the OP is saying that the friend used Windows 10 System Restore this has no impact whatsoever on an individual's personal data files created after the restore point being used. All user data is maintained, it is only the state of the operating system that is restored.
If, on the other hand, he or she did a restore using a system image from an earlier date, that does overwrite everything and you'd have to use recovery tools to discover what can be retrieved, if anything.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
Memory is a crazy woman that hoards rags and throws away food.
~ Austin O'Malley