S.K.
C.,
This works well, but it's not popular advice. Her parents are going to have to wake her up during the day. They don't need to keep her up all day, but they do need to wake her for at least 20-30 minutes every 2-3 hours. Change her diaper, play with her, tap her feet or run a gentle finger up and down her spine, whatever it takes. When it's night time, they lay her down (even if she's wide awake) in a dark room and leave. There is no need for a nightlight. She's not afraid of the dark yet because she just spent the last nine months in pitch black.
When she does wake up at night, only turn on as much light as you need to find her, nurse her and change her - maybe a light in the hall and the door left open a crack or turn on a nightlight. Don't play or talk, just nurse and change diaper quietly and lay her back down in totally dark, quiet room and leave.
Good luck,
S.