Ma Shail putri(Parvati) is worshipped on first day of Navratri. The name itself means Daughter(putri) of Mountain (Shail). Many people believe that Goddess Parvati got this name because she was the daughter of King Himavan bet there is one more story associated with this name of Devi Parvati.
Once when Devi Parvati was a kid she was playing hide and seek with her friends. Her friends were hiding and she was searching for them. While searching she saw a river with beautiful lotus flowers. She was about to pluck a flower when a cow came to her. It seemed to her that the cow was in extreme pain. She wanted to help her so she went on with the cow.
At some distance she saw numerous bones and carcasses of cows scattered on the ground. It looked like someone had killed and eaten them recently. She touched the head of a cow and closed her eyes. Then she got and insight about demoness Tarika, sister of Demon Tarakasur. Tarakasur had a boon that he could be killed by the son of Lord Shiva and Devi Parvati only so he sent his sister Tarika on earth to kill Devi Parvati. When she came on earth she saw all these cows and was tempted to eat them and attacked those cows. One of the cows escapes and went to Devi Parvati.
Parvati made a plan to kill the demoness. She took the form of a small hill (shail) and asked the cow to hide behind her and moo to entice Tarika. The cow did as asked. Tarika tried to attack the cow but Parvati in the form of hill shifted her place and protected her. She again tried to attack the cow but Parvati again sheltered her. This hide and seek kept on going. Meanwhile Parvati’s father and friends got worried about her as the sun had set and it started growing dark. Her father and many villagers came there and witnesses the struggle between the cow and the demoness but they failed to find Parvati.
Now Tarika got furious and took out her sword to break the hill. On seeing this Parvati’s father also took out his sword. Before any of the two could attack the hill started breaking emitting divine golden light. Soon everyone saw Devi Parvati coming out in her divine form with a golden crown on her head and trident in her hand. In no time she slayed demoness Tarika. Everyone started praising and applauding for her and offered lotus flowers to her. Looking at her in this form her father named her Shail putri.
This form of Devi holds a trident in one hand and lotus in other and sits on a bull. In this form she also blessed the cow that like herself cow will also be worshipped as a mother. That ia why cow is highly revered in hinduism and considered as mother.