firm things which show 3yr old needs treatment?

hi there,

My daughter is 3 years old, she is been diagnosed with abnormal x-ray and the doctor felt suspicious about TB, done the skin test which came as negative and doctor advised to do BAL and the culture result came negative as well.
the latest x-ray which was taken shows abnormal and the doctor suggested to treat this as TB.

My daughter is gaining weight and didnt shown any symptoms.

I am bit curious about this whether is there any firm things which shows that she needs to be treated.

Could someone shed lights on this?