a) Soha in only 6 and doesn't need to be burdened with the truth
b) Truth is bitter - just because the poor child had Khada doesn't mean she will take all things bitter.
c) Sona is not the one to pour her heart out to a little girl. Soha is her child not her best friend.
d) Sona isn't intrinsically capable of talking about things that hurt her. She always tries to find a way. Haven't we learnt this so far? Isn't that why she never went complaining/ discussing/ pouring heart out to Dev?
e) This serial is about how faith and trust have their boundaries and repeated lies does ruin your reputation. i.e., don't go around saying I can read your heart, read your mind, you are my heart beat, etc when you can't speak the absolute truth to an adult.
If Sona spells it all out, what is left to show?
Enjoy the ride, just switch off your intellect!