I am having the same problem! Tulip was doing REALLY well with the whole biting thing until today! My daughter had a friend over and they were playing with her in the bedroom while I helped my hubby pull a tub out of the basement we were taking to the garbage..(long story!) Anywho, my daughter comes out and says Tulip is biting really hard again! I was really shocked because we had worked so hard with her to get her to stop... well I found out later the friend was grabbing her and holding her tightly in her hands..
GRRRRRR!! I was really mad at the girl and kinda mad at my daughter for not standing up and saying "DON'T DO THAT!" Needless to say.. NO MORE FRIENDS will be holding her!! So anywho, we are back to square one! The only way I have been able to stop the biting is by first saying "NO Biting!" firmly then placing her in a small carrier we have and putting her in a quiet dark room for 5 min. with no interaction from anyone in the family. I time it exactly. So far it seems to work for us. I also try to do this fairly quickly after the bite so she realizes that is what caused her to be placed there... I hate doing it though, but the unstable perch and just saying NO doesn't seem to work with her either!