Thanks for your query.
Is your granddaughter a mouth breather?
If your granddaughter is running fever
and has not eaten very little then it has to be ensured that she takes a lot of liquids. Occasionally because of less fluid intake during fever tartar
can collect aroung the teeth. It is very difficult to explain the black spot in the roof of the mouth and the upper teeth.
I suggest that you ensure that the child brushes her teeth and observe if the black spot(s) have disappeared. In case they persist then it is better to consult a doctor.
Wishing your granddaughter an early recovery.