I went deaf suddenly in my left ear years ago. I went to bed one night and woke up with my ear feeling plugged. I also had terrible vertigo and tinnitis (ringing). The Doctor did tests and I was classified as profoundly deaf just overnight. No one really knew what had happened. It could have been an anuerism or vascular spasm. The Doctors at that time said that 2/3 of the people that this happens to will regain their hearing. I was not so lucky. I do have Celiac disease (wheat allergy) so maybe that had something to do with it. I also have suspected parasites. At this point only God knows. I hope your Daughter is ok and regains her hearing.
Did they check for nerve damage? If there is no damage to the inner ear bones or to the tympanic membrane then nerve damage would be something also to look in to, possibly from a viral infection.