Polycystic Kidney Disease (PKD) Support Group
Polycystic kidney disease (PKD) is a progressive, genetic disorder of the kidneys. It occurs in humans and other organisms. PKD is characterised by the presence of multiple cysts (polycystic) in both kidneys. The disease can also damage the liver, pancreas and rarely the heart and brain.

I think the most important thing for your daughter is to have a healthy lifestyle and I would suggest to check her bloodpressure regularly even at this age. It is thought that children with PKD can already have (asymptomatic) hypertension and if that's the case treating hypertension will postpone the deterioration of kidney function. Chances are 50% that she has it. I found out in my twenties that I had this disease. I had problems in pregnancy, severe hypertension.
If she has not the disease it is also good to have a healthy lifestyle.
I just found out my eleven year old son has it had well. He has hypertension. Today we went to see the nephrologist. His blood pressure was 130/78 while it should be 100/60 at his age. He will get medication probably. I am very sad about it but try to learn him that life is not over with this disease, but it is definately more difficult...
Regards Nicky
My kids are older teenagers now and there definitely comes a point when you lose control of some of and eventually everything that they eat and drink ( an do!) you can't actually do anything about that except continue to give good examples and advice. Hopefully they retain the teaching that you've provided and come back to it at some point if they stray during these years.
With regard to diagnosis, it is sometimes possible to diagnose the condition when very young, but just as likely is that it can't be detected on scans until later. A negative diagnosis means nothing until after age 40. As Nicky says, it's good for everyone to live a healthy lifestyle, so just keep promoting that message.