Understand that the more your friend uses the computer the less chance of data recovery. This is because deleted areas in the file system are used by other processes. In fact if the lost data is very important it is safer to try recovery where the drive is removed and connected to another PC for recovery. But recovery firms charge high fees and it is better to research the subject (forensic data recovery) and try yourself. .
Start by looking in the Trash bin in case the files are sitting there.
If you are willing to accept the risk that the disk might be overwritten try these utilities …
If this risk is too high stop using the drive and more advice can be offered.
[Added note] There is a chance that the files might have been moved rather than deleted. If a unique filename is known try searching through the entire file system where it might be buried away. Some detective work is needed. Can you view the recent history of commands?
[Further note] I have just read from here …
that a similar loss of data was discussed back in 2014.