Answer: Yes, the senior can amend her FAFSA. In fact, she must amend it. There’s some info here that explains the requirements and the process: https://studentaid.ed.gov/sa/fafsa/next-steps/correct-update. Changes in dependency status (such as becoming an unaccompanied homeless youth) are a required update. The student needs to go to fafsa.gov, log in, click on “Make FAFSA Corrections,” enter the FSA ID (username and password), and change and submit the information. This can be done on paper, too. Depending on how far along the student is in the process with her university, she also could contact the financial aid office there and ask for their help making the changes.
Also, make sure the student has the verification letter from you (regarding her status as unaccompanied and homeless), and that you also are ready to provide a copy if contacted. As you know, the process doesn’t go as smoothly for many unaccompanied youth, and things like changes in status sometimes even less so.