I think you posted this question a few days ago and I replied there but once again, take your child to a different cardiologist, you need to get a second opinion. I'm not a doctor but I do have a heart baby and was asked by our cardiologist to run a support group for other parents at the hospital. All the symptoms you describe can be related to the atrial septal defect alongside other symptoms such as getting overly sweaty around the back of the neck when she feeds, and do her hands and legs gets cold or very mottled? They are all warning signs alongside the weight issues and the blue lips. When she was in hospital did they have her attached to an oxymeter to measure the amount of oxygen in her blood? That would give you a good idea of whether her heart is working properley. As for the weight have you been refered to a dietician yet? If not ask to be, they can give you high calorie supplements for milk and also help you later to sort out a diet with hidden calories such as cheese in mash potato made with cream not milk etc. At least if you can help her gain some weight on then she can get bigger and stronger until she finds her own appitite. Best of luck :)
I don't know what to say, but my heart breaks for you and I will keep your little girl in my prayers. What is her name?