Fortunately this question was asked to Sri Aurobindo though in different words. We have a clear, concise and complete answer from him on this issue. The letter is as quoted below.
‘In the Chandi the names of the four Cosmic Powers of the Mother—Maheshwari, Mahakali, Mahalakshmi, Mahasaraswati—are mentioned along with others, but the name Radha is not mentioned. This is a clear proof of the fact that when the Chandi was composed the Radha-Power was not manifested to the vision of the saints and that the Chandi mentions…