The chances of having nightmares significantly drop when you clean and protect your aura before going to sleep, and when the room or home your sleeping in is spiritually clean.
If your coworker isn't a spiritually inclined person, a few material tips would be to make sure their home or room is picked up; having clutter in the home can fog the mind. What they can also do is set up an alarm in the middle of the night, have them stand up and wake up for 2-3 minutes and then go back to sleep; this method increases the chances of them being able to control their dreams.