Sheneedshelp - Absolutely I would delete her. As a further step I would (and have) deleted my entire facebook account. I was friends with many of my kids' friends and, honestly, it very much disturbed my own sense of peace and serenity to see the kind of sh*t they were up to. I mean, I can't control it, it disturbs me greatly, so what on earth is the point of watching it unfold every day? I don't miss facebook at all. The people I really want to stay in contact with, I can do in a million other ways.
Remember that you didn't let Amber go because you were trying to control her choices. You let her go so that you could properly concentrate on nurturing your younger children and yourself. Take whatever steps necessary--every minute of every day--to ensure that is what you are doing. In just a week or two you will be amazed at how much better you feel and you'll know that it's the right thing.
What other steps could you be taking to protect yourself?