Disk full. Can't move files to trash.

Is there is anything in the trash, try emptying the trash to get more space.

Try booting into Safe mode, by holding the “Shift” key during boot.

This will clean some cashes, that may free up so me space.

Finally, start an Applications -> Utilities -> Terminal session. Enter

rm

Enter a space after the rm

Drag & Drop a file you want to delete from the Finder on to the Terminal window.

Enter the return

That should delete that file. It will be deleted immediately! So make sure you want it to go away.

Wash, Rinse, Repeat to delete additional files.

That is NOT the only way of fixing this issue. Saying that none of the files can be recovered at that point is very misinformative and could quite possibly screw things up even more for some. I had the exact same issue and for me it was enough to just boot my MacBook up in safe mode which cleared the caches and freed up some space. A lot easier, safer and quicker thing to try before resorting to something like a full wipe & reinstall.

No need to jump directly to this extreme. Reboot in safe mode and you should be able to delete some files to make space. Just worked for me after I thought all hope was lost.

You will have to erase the drive and reinstall macOS. None of her files can be recovered at this point. You can remove the drive and put it in an external enclosure so that you may try recovering her files with recovery software. I'm afraid you have no other alternative at this point. In the future, she should leave at least 10% of the drive's capacity as free space to avoid this problem.

General File Recovery

If you stop using the disk it's possible to recover deleted files that have not been overwritten by using recovery software such as MAC Data Recovery, Data Rescue II, File Salvage or TechTool Pro. Each of the preceding come on a bootable CD to enable use without risk of writing more data to the disk. Two free alternatives are Disk Drill and Cisdem DataRecovery. Recovery software usually provides trial versions that enable you to determine if the software would help before actually paying for it. Beyond this or if the drive has completely failed, then you would need to send the drive to a recovery service like Drive Savers, which is very expensive.

The longer the hard drive remains in use and data are written to it, the greater the risk your deleted files will be overwritten. Also, visit The XLab FAQs and read the FAQ on Data Recovery.

Install El Capitan or Later from Scratch

If possible backup your files.

1. Restart the computer. Immediately after the chime hold down the CommandandRkeys until the Apple logo appears. When the Utility Menu appears:
2. Select Disk Utility from the Utility Menu and click on Continue button.
3. When Disk Utility loads select the volume (indented entry, usually Macintosh HD) from the Device list.
4. Click on the Erase icon in Disk Utility's main window. A panel will drop down.
5. Set the Format type to Mac OS Extended (Journaled.)
6. Click on the Apply button, then wait for the Done button to activate and click on it.
7. Quit Disk Utility and return to the Utility Menu.
8. Select Install OS X and click on the Continue button.

This will install the version of OS X you had installed.

Because you did not include specific information on the computer model or the installed version of macOS, I don't know if the above instructions will work. If they don't apply to your machine, then please provide the needed information. To find the model identifier open System Profiler in the Utilities' folder. It's displayed in the panel on the right. You may also find the complete model information by selecting About This Mac from the Apple menu.

Kappy wrote:

Then mark Bob's reply as Solved. He will appreciate it.

DeltaSierrah is not the thread owner, plus I don't need extra points, as much as the confirmation that my suggestions worked for yet another user.

I'll get my next 14 points so I hit 25,000 soon enough. But I do not think I'll get anywhere close to your ~300K until after I retire from my day job 😁

This worked for me, thanks!

Then mark Bob's reply as Solved. He will appreciate it.