Rivendare Server. reports from every person inside the instance says nobody can loot her =( The bag cursor shows up when you hover over her, and she's all sparkly and dead. but when you loot her nothing shows up =(
After a while (somewhere between 10 minutes and 2 hours) it does become lootable and everyone is able to recieve badges/hand out loot.
It's been suggested throughout Onyxia's Lair general chat that having the loot set on Group Loot instead of master looter is the cure to this. So please just make sure it's on group loot before you kill her =(
Not sure if this is just a Rivendare server issue or not, but thought i'd share the issue.