Shyaamala is the Shakti of Sada Shiva. She has the form of Shuddha Vidhya and Ashwaaroodha. Brahma, Vishnu, Rudra, Maheshwara, Sada Shiva are called as prancha(Five) brahmas. Sada Shiva is the fifth one of these. Here his Shakti is being described as one of the forms of Divine Mother. This Shakti is called with names such as Aditi, ida, Saraswathi in vedas. Raajarajeshwari, Shuddhavidhyaa, Ashwaroodha and Shyaamalaa are all part of Sada Shiva's family. Hence she is called Sada Shiva Kutumbini.
Sada shiva is the principle tatwa of shiva where one experiences oneness with the universe. When a yogi experiences 'Aham idam' or I am this universe, that stage is called Sada Shiva.