Oh dear, poor Betty. She sounds in a very bad way. If she has a respiratory illness, its vital not to delay due to the nature of birds air sacs which are all over their body, making this a serious illness. Can you separate her from the others eg in a cat box with her own water and food, to give her a rest and tlc and to stop it spreading? I am not sure what you mean by MG, but if you mean micoplasma, this is treatable with antibiotics if you act quickly. I would also give her lots of berries and a vitamin and mineral supplement.