No, of course, it is not an adjective, it is a noun. You can see it easily from its ending. If it were an adjective, the ending would be -ая.
Just the noun in this case functions as an apposition Apposition - Wikipedia, the free encyclopedia.
Some more examples of appositions: красавица Оля, студентка Наташа, мой друг Андрей, профессор Иванов, красавица ёлка etc.