Hello, McCarthy Forester.
Reboot into Safe mode (hold the shift key down at startup) and see if you can delete the account while logged in that way. It takes longer to safe boot so be patient.
How to use safe mode on your Mac - Apple Support
Safe mode forces the OS to clear certain caches and logs and do other miscellaneous housekeeping. It's non-destructive to user data so is safe to do. Very often certain weird software behavior is corrected by simply logging in this way as a troubleshooting method. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's normal.
Does the problem persist while in Safe mode?
Exit safe mode by restarting your Mac normally and re-evaluate the issue again after a normal reboot.