I've always felt it was ridiculous to punish the whole because one did something wrong.
Also, my youngest will always step up and take the blame no matter whether she did it or not, because she doesn't want to get stronger consequences. And my oldest is the most stubborn kid in the world who will sometimes deny doing it no matter what the punishment, just to let his sister get punished with him.
If I were in your place, I would take each of the younger two aside and speak to each of them privately about respecting other's belongings. I would say something like this...... (yeah, I know, it's pretty heavy on the guilt trip, but it usually works).......
"You know, Sister C. I don't know who wrote on Sister A's ___. I don't know if it were you or Sister B. -- No, you may not say anything right now. This is my turn to talk, and your turn to listen only. -- I thought I had been raising you girls to respect other's belongings. Apparently I'm not doing a very good job as your mom. Because one of you wrote on your Sister's ___ and has made her very upset. I know you wouldn't like it if someone did that to your ____. I'm so disappointed that either of you would treat your sister like that.
And, even worse, one of you is lying to me. And I am so hurt, and so sad, that either of you would lie to me. The worst part of lying is that now I will have trouble believing you when you tell me something. I won't be able to trust either of you for a long time. Trust is something that has to be earned back. And because I don't know which of you is lying to me, I won't be able to trust either of you. That makes me so sad, that you would not respect me enough to be straight with me. And it makes me sad that I cannot trust my own daughters. Trust is so very, very important. When you have someone's trust, you earn their respect and admiration. It's so important in life to deserve others' trust. When you lose someone's trust.....(and here I would shake my head slowly and sadly)......sometimes you never get it back. You've lost it forever.
Remember what I've always told you.......if you do something wrong, it is far better to own up to it, and take the punishment. Because if you don't take the responsibility for your actions, and I find out later that you were the guilty party, your punishment will be far, far worse. Now, that's all I'm going to say about this incident. I hope that you will think about what I have said, and know that you can still do the right thing, if you know what happened to Sister A's ____.
And now, I'm going to go out and buy Sister A a whole brand new _____ to replace the one that was ruined."
Hopefully one of them will say something that will lead to the truth.
Good luck.