Admin login username empty
I am writing for my sister, who cannot login to her Macbook Air running OS 10.7. She installed an Adobe update of some kind, and when the computer restarted, it took her to a gray screen with just an Apple logo and two white fields for Username and Password. She does not remember her Admin username, but has tried all usual suspects. The only other options appear across the bottom: Sleep, Restart, Shut Down.
Is there a way around this screen? A universal login name? A way to restart and get back to the original login screen which allowed her to select her Admin account? Any ideas?
MacBook Air, Mac OS X (10.7.1)