They could have suspended the employee from work pending their receipt of the test result. They could have fired her for not returning the test result on time. However, as they did not, they must pay her for the hours that she worked.

If the employer cannot be convinced to pay, the employee can file a wage complaint with the State Department of Labor. She may want to consult an employment lawyer to discus her options if her employer retaliates for her making a report. Forms and contact information can be found here.