Madame Fox is look for students to join her team. If you have completed the course, that means all of the lessons plus the extra credit. If you have done this, then feel free to try out for the team. Being a PA is a privilege, not a right. During your time as a PA, you will be expected to dedicate a certain amount of time to the grading of assignments.
If you have any questions you can contact me and I will be happy to help.