She will have to file a petition with the court to seek Emancipation. She should consult with an experienced Family Law lawyer like to myself to assess her chances of success at seeking Emancipation (for example, she will have to prove to the court she can be financially independent). I wish her all the best of luck. Warmest regards, Matt Catchick.
She probably will not be allowed to leave unless the Court determines that she live by herself. Perhaps the adoptive parents can come to some sort of agreement with another family in the area for the time until she becomes an adult. I would consult with an attorney to discuss your options. Best of luck to you.
This information is provided as a public service to provide a general answer and should not be relied upon as legal advice.