Check the belly area behind her legs. Is it soft and pliable or swollen, firm and hard. I had a few birds that had fluid build up in their abdomen, a condition called ascites. The fluid will build up until they suffocate. This is caused by a disease of some internal organs. If this is the case you could extend her life by draining her abdomen with a large needle and syringe. There are some videos on youtube. It is a tricky procedure and could actually kill her if the needle punctures her intestine or other organs. So you wouldn't want to do this unless you are sure that ascites is the problem.