Thanks for writing in.
Several laboratories do a test which allows them to detect which substance is your daughter allergic to. They test quite a few substances. Please get it done. Ask
her paediatrician about cromolyn sodium nasal spray
as that will prevent allergies.
The only permanent solution is avoiding the allergen totally. Since this may not always be possible, please make sure you keep your house clean; change the pillow covers daily; wash the bed linen in hot water and keep a humidifier in the room.
Hope this helps.