I am sorry to note that you are having a tough time.
The congenital heart disease
with TOF does not help although it is more likely that she has a viral infection and unable to shake this off.
This is very common in little children and more so with yours who has a CHD.
Azibact will help but of course is just for this infection.
Please ensure all immunizations are up to date.
I am sure all of this will settle down once she has gone through the surgery.