1 yr old cardiac patient with low weight, too many doctors and frustrated parents HELP!

My 1 yr old grandaughter was born at 36 weeks and had to have 2 heart surgeries to repair coarctation of the aorta and baloon angio to fix her mitral valve.  She was in the hospital for 8 weeks after she was born and we were not able to feed her normally (via mouth)  for most of the 8 weeks.  We had to go to speech therapy to teach her how to suck and swallow.  She seem to be developing normally (sitting, crawling, trying walking, talking) Now the doctors have sent her to an endrocrinologist due to her low weight (15 lbs @ 12 months).  They keep doing blood tests.  

My question is this - could it be normal for her to have this low weight because of the other problems and constant medical appointments, fasting tests and surgeries?  Where do we draw the line with all this medical testing?  

She has a cardiologist, a kidney dr, a pediatrician, an edrocrinologist, and multiple lab and diagnostic appts.  It is so very hard to keep her on any type of regual schedule with all the appointments.  She hates the blood sticks.  The doctors don't seem to communicate with each other (one tells me one thing the other tells me something else),  The doctors don't seem to remember any of her history when we come back we have to go through all the surgeries and tests with them at every visit (I think I keep better records).  Sometimes they want to send her for tests she already had.  How many chromosome tests should she have?  This is getting ridiculous and nobody seems to listen or care, just schedule more stuff.   The family is at our wits end with this medical red tape - How do we get control?