Sri Radha is para-shakti. The supreme shakti. She is the source of all the Lakshmis. Some may refer to shakti as Lakshmi or Durga but Sri Radha is the absolute shakti. Sri Radha is the height of the supreme shakti or para-shakti. Sri Krishna is shaktiman while Sri Radha is shakti.
Sri Radha is the gem of Mahabhav. Mahabhav-svarupini, the personification of the highest form of love. She is made of Mahabhav. She is the essence of Hladini shakti and the personified form of Madan Mahabhav. Hladini shakti personified (supremely blissful potency). Sri Rupa Goswami refers to this as Madanakhya-Mahabhava. Madanakhya-Mahabhava is the unique experience of Sri Radha.
Sri Radha has a molten gold complexion. A blue garment since Krishna is blue, and a red upper garment which is made out of deep love (anurag). Sri Rupa Goswami has cited 25 special qualities that mesmerise Sri Krishna.
Taken from Radha-Tattva by Sri Ananta Das Babaji