Congenital heart defect

My niece was recently diagnosed with a congenital heart defect.  Because I don't live close by, I am getting my information on what is going on from my mum, who is having trouble remembering all the details and the name of the condition.  I obviously don't want to bother my sister at the moment - se is at the hospital all the time and has enought to worry about, but I do want to know exactly what is going on.

From what my mum said, she was born with only one ventricle and will need a series of heart operations which will leave her with one ventricle and one atrium and change the way the blood goes around the body, and that later on she will probablt need a heart transplant.

From a bit of googling it sounds like hypoplastic left (or right) heart syndrome, and I have got a lot of information about that.  The only thing that confuses me is that the websites all say this condition caues the baby to be in critical condition in the first few days or a week and that it is usually diagnosed either prenatally or on the first week.  My niece wasn't diagnosed until she was two months (after suffering weight loss and a urine infection) - is this possible with HLHS?

Hope someone can help.