If time is the problem, then tighten the belt and reduce work study hours or drop work study for the semester.
Organize and prioritize. I had one who took between 21-24 credit hours every semester the first two years. As soon as the books for a class was posted at the bookstore website, I searched the internet for the best prices and ordered books. When they arrived she started reading them. This way she was ahead in reading before classes even started. Once school started she worked ahead as much as possible. This way if she needed a sick day, she could just sleep and not be behind. She also prioritized her classes by credit hours. An A in a 4 credit class is worth more than an A in a one credit class. This way is she needed to slack off in a class it was the 1 credit class.