Hi and welcome, Your child is suffering from streptococcal pharyngitis. it is a bacterial infection leading to inflammation of mucous membrane of the throat and the tonsillar crpts. It often shows symptoms of cough , fever , nasal drip , pain and swelling in the throat , difficulty in swallowing and production of phelgm. brownish dark green colored mucus you have mentioned is nothing but phelgm . Since your daughter is too young i suggest you to consult a pediatrician and get the clinical evaluation and diagnosis done and then go for treatment. Till then you can give her soft food , avoid sour and spicy food, avoid citrus juices and cold water , give her distilled or boiled drinking water instead. Mouth gargling with lukewarm saline water gives soothing effect to the throat. take care.