Welcome to SR. What you can do is find out what resources the rehab offers to families and start attending Alanon meetings. Coming here is a lifeline for many of us.
What Afraid2 said about a aftercare plan is usually how these programs work. My son was an adult by the time he entered a program, so things were handled differently. Most places for teens involve the parents by requiring parents' meetings and working with the counselors too. If her program doesn't offer this, you might want to find an Alanon program that other parents of kids from her rehab attend.
I think you have the right idea about abuse/addiction and that's good progress for you. There are lists of suggested reading material in the sticky threads on this forum that are very helpful.
As overwhelming as this all is right now, and I won't sugarcoat the facts, addiction is a progressive disease, but it can get better- for YOU- regardless of what is happening with your child.
Sadly, too many moms and dads have experienced what you are facing now, but the good thing to know is that you never have to face it alone. I'm glad you found SR.