The Marhaba lounge while not amazing is not bad at all. If she just wants a place to sleep, DXB has some nice "lounge" chairs in the main terminal and at 5 or 6 she should be able to easily grab one. She won't be able to get up from the chair though because by 9 or 10pm people will be hunting for them.
There is also Snooze Cube (in T1 I think I saw it)
http://www.snoozecube.com/?page_id=596