Morrígan

Winter Goddess (冬の女神 Fuyu no megami): is one of the old gods of Winter and Death.

Background
The Winter Goddess is first mentioned just before the night of Yule, an important cycle of the year that showcases the shift between the winter and the coming spring, by the Twins of Yule and later by Elias. The Winter Goddess later seen riding ontop of another god, it's revealed that she's pregnant as she unknowingly passes by Elise, Chise and Ruth. Before leaving she takes notice and picks up a mistletoe.

The Winter Goddess later appears again before Ruth as he searches for Chise, being first mistaken to be the Slay Vega before Ruth gets a closer look at her and sees a resemblance between her and the Winter Godess from earlier, quickly deducing that this must be her daughter. The Winter Goddess learns that Ruth had offered gifts to her mother, the mistletoe, and as thanks she decides to help him by lending Ruth her "flame", which reveals Elias position to him. Ruth says thank you before leaving to find Chise, the Winter Goddess replies only that next winter, when she's her mother, she asks only for that which Ruth offered her then.

Trivia

 * The concept of the Winter Goddess is a slight alteration of the Goddess of Yule, a being that becomes the Great Mother before giving birth to the new Sun Goddess.