What should she do now?
Students can email help@virginia.edu or call 434-924-HELP (4-HELP when on Grounds) when there are issues with SIS. That info should be on the SIS login page as well.
My daughter could not do her registering at midnight either because the system crashed. We set the alarm for 3:00 Am, and by then some of the classes were full. She was able to swap a class, so that worked:).
Thank you, Dean J and oldUVagrad! Everything ended up working out for my daughter as well. She was able to get in at around 11:30 pm (or so) mountain time (which would be 1:30 eastern), and she got some wonderful classes spread out throughout the week perfectly. 
Mom (moi) just had a little panic moment…I should’ve known better…she’s my fourth (and second at UVa).