"DD I am so sorry that you have been in this situation. It's important to me that you know that I do not, in any way, hold you responsible. And I completely understand that you must have had conflicted feelings about what you knew, and if you have been feeling divided loyalties, that would be completely normal, and I understand."
OP, please don't pepper your daughter with questions, as much as you'd like to know. She is in a bad place. (As are you, and my heart goes out to your family.)