It sounds, from your description that her father has a reason to avoid contact with government officials. You have offered several reasonable accommodations, transportation, etc. to help him enroll his daughter and he does not want to be "found".

You are an angel to help her! Several people have come forward with contact numbers and legal information regarding help for homeless teens. I hope you can get some help. She is an at-risk teen and anything that can be done to rescue her is a blessing.