Question: How do we know, what is related to what?

So today, is a very special day to me... it is the first time we took our baby girl home... 3yrs. ago! We were petrified of what we were about to learn... we had no clue at this point, that Jilly would be here with us 3 yrs. later... I am so thankful for these past 3yrs. I have learned so much, met so many new friends, and learned how to be strong, thanks to my little hero: Jilliann Rose!

Today, I am thinking about what Noah's mom mentioned... how do we know what is stroke related or CHD related? I find my self, asking our Physical Therapist that question all the time! Jilly also has neuromuscular issues, believed to be congenital; causing her to have hypotonia (low muscle tone) otherwise known as a "floppy baby". The only dx. we have so far is periphreal neuropathy (meaning the nerves coming from her spine to her limbs-arms and legs). So you take a child with a bad heart/and bad nerves/who has had a stroke/ and has spent 1/3 of her life in a hospital, another 1/3 home recovering... that only leaves 1/3 of her life, to work on developing in all areas of life...
So, how do we know???
I think maybe, we can't know... we can guess, asume, and sometimes even hope that a certain symptom is related to a certain cause... because that would be the better choice!
We have been blessed on one issue of stroke.. the" tightness", because of Jilly's "looseness" she was born with... it counteracts the tightness that should of been on the Left side of her body, making that side more like normal. But, the two sides of her body, are not equal... the right side being floppy from low tone. I cannot imagine if the two sides of our body... were so different, and yet our STROKE kids seem to learn to compensate... even to the point where only us and their therapists know the difference! Then there is the heart issue... is the weakness, because of fatigue due to low heart function or poor oxygen levels?
I think that must ALWAYS play some part in any issue. Who does not feel weak, when they are not feeling well!!! Jilly is 2 months away from heart surgery, the Fontan... I hear from more experienced moms, that I will see a difference in strength and endurance... along with better color... so I guess I will soon see, how much the heart... is making a difference!
What do you think???