According to the Saraswati Ashtottara Shata Namavali(108 names of Saraswati) found here ,one name of the Goddess is Shivanuja(9th name in the list) which means "One who is the younger sibling of Shiva"
शिवानुजा Shivanuja ॐ शिवानुजायै नमः। Om Shivanujayai Namah। The Goddess Who is the Younger Sibling of Shiva
What can be the possible explanations behind this name (because we usually don't consider Goddess Saraswati as Lord Shiva's sister)?