Maa Siddhidatri may be the ninth avatar of maa Durga which is worshipped over the 9th working day of navratri. Ma Siddhidatri is represented with 4 arms sitting down on a good looking lotus flower. While in the Srimad Bhagavatam, a summary of fourteen various names are specified for Durga. https://www.youtube.com/watch?v=S1HpMpEww4Q