It could be that while doing the test there was one or more technical issues. The test asks you to take a picture of your ID card then your face. It also takes multiple pictures during the test. If she forgot to take a picture of her ID or face, then the officer could have not accepted the test. Another possibility and it's very common, is that the webcam was not working while taking the test. There is a small box that appears on the page where she could see herself while answering the questions. If that was not working, then the officer likely didn't accept the test.
She can also send an email or call IRCC to know more about the re-test, but I'm 90% it's technical issue.
Good luck to her!