I gently suggest that you put your focus on your two younger children. Amber is going to do whatever Amber wants to do. You cannot help her, but you can help your other children. They need you to guide them and to be your main focus.
I do hope you will get to an al-anon meeting and keep going. You really need some face-to-face support from other parents who have children who are going headlong down the wrong path with alcohol and drugs. While you cannot save Amber, you can learn how to save yourself and gain some peace of mind and serenity.