is unlikely to cause her tightness in throat.
With the history given by you it is not possible to say what causes her symptom. Because there are many causes producing this symptom. More details are needed like her age, how long her symptom has been, is the onset sudden or gradual, has she had common cold
at the beginning, has she has any nasal symptoms at present also, has she has any heartburn
and so on.
When you say she has bacterial or viral infection, what is it exactly - common cold, fever
As Paediatric Gastroenterologist has seen he/she would have got all these informations and most probably he/she is right in advising scopy.
However it is advisable to take an opinion from an ENT specialist
before going for scopy