Based on the thread posted on the other site, there was indeed a cause for the change in the Iguana's behavior. She seemed to indicate that she had a new roommate, so jealousy would seem to have caused the attack.
It's very common in animals that have been hand raised to be possessive of their owner -- as well as get upset with the owner if it's getting less attention for whatever reason.
Umbrella Cockatoos can be very loving birds, but many times they can attack and be quite vicious if they feel they are being neglected or if they are jealous.
I've noticed with many animals it comes down to how they are raised. If they are raised by one person, jealous behavior is more likely. However, if they are raised with attention from multiple people, they are more likely to adjust to new people in the future.
Scary bite though. I think getting bit in the face is about the worst place to get bit. At least if it's on your arm or leg, you won't be reminded about the event every time you look in the mirror.