Was this the baby you were feeding mashed fruit to? I'm sorry to say this, but I suspect she died of malnutrition or starvation. Fruit contains a lot of water, sugars and some vitamins and minerals. It doesn't contain the right proteins, good fats or carbohydrates that a bird - especially a growing bird - needs to survive. This is why it's very very important that a baby bird is fed a formula diet until it weans itself and starts eating a balanced adult diet.