Answer: She cannot complete the FAFSA as an unaccompanied homeless youth, because she would’ve had to have been in that status after July 1, 2017. However, she still qualifies as independent because of the guardianship. See: https://studentaid.ed.gov/sa/fafsa/filling-out/dependency. “Has it been determined by a court in your state of legal residence that you are an emancipated minor or that someone other than your parent or stepparent has legal guardianship of you? (You also should answer “Yes” if you are now an adult but were in legal guardianship or were an emancipated minor immediately before you reached the age of being an adult in your state. Answer “No” if the court papers say “custody” rather than “guardianship.”)”
She can check that box, and then fill out the FAFSA just like your unaccompanied youth— using only her information.