Find out if the American Embassy has a contact line for family of victims. They can give you information regarding where to find out about the injured. They may also be acting as liason for American citizens trying to let their family and friends know they are alright.
If the American Embassy can not help you could try the British Embassy.
If your daughter uses credit cards or her cell phone you might be able to get info from the credit card or cell phone company as to when and where they were used last.
You would have to explain the emergency involved. They still may refuse to give you the info. But it is worth a try.
My hope and prayers are with you.
Thanks for the advice - I'm Australian and I have made the correct moves with DFAT here.
She's not on any current lists of injured, dead, or missing, neither are any of her friends. The good news is that she was in a group - if a group of Australian girls were involved, we'd expect that to be quite big news. The fact that there is nothing means that hopefully they are all OK.