Vaishno devi is one of 108 shakti peetha, the story of Vaishno Devi is found in Chandi uppurana. When Vishnu Bhagwaan cuts Sati Maa's body into 108 peethas then 52 body parts fell onto earth atmosphere and rest of the 56 fell on other planets. Out of which the "Blessing Hand" of Goddess Sati had fallen on "Planet Venus" or Shukra. Goddess Lakshmi is considered to be the ruling planet of Shukra hence also known as Goddess of Venus.
But in the beginning of Treta Yug, there was a devil called "Mur", he got the boon from Brahma that he must not be killed by any human being, god, trinity, or any one born on Earth. Eventually in a gods-demon war, Demon Mur ran behind his greatest enemy Vishnu, who went to the place where was the shakti peetha of Goddess Sati on the Planet venus. Goddess Lakshmi insisted goddess Parvati, the next incarnation of Adi Parashakti after Sati, for help, thereby goddess Sharda and goddess Parvati in the form Kalika, went to the region.
Goddess Lakshmi incarnated in spiritual form, because physically, she had already been taken birth as Goddess Vedavati who later on would become Sita in next incarnation. So Mother Parvati herself gave her physical appearance, with a soul of "Lakshmi" and Goddess of knowledge, Saraswati. The girl born was named "Kumari". Saraswati, Kali and Lakshmi dropped three pindies (Sacred stones) as their true forms, where they will be present till the end of Kaliyuga. To make the devil not known about the birth of the miracle goddess, Lord Shiva Shifted the mountain to Earth. When the devil entered the place who was running after Lord Vishnu saw a little girl. She killed him and there by, Vishnu got another name called "Murari".
Since her soul was of Lakshmi so she wanted to have Vishnu as her consort. She incarnated in the house of Lord Ratnakar, this time Narada named her "Trikuta" also by the names kumari etc.
The girl right from her childhood displayed a hunger for knowledge which was like a vortex and which no amount of teaching and learning could sufficiently satiate. Subsequently, Vaishnavi started looking into her inner self for knowledge, and soon learned the art of meditation and realized that meditation and penance only could bring her close to her greater objective. Vaishnavi thus relinquished all household comforts and went deep into the forest for Tapasaya (meditation).
When she heard that Lord Rama moved to forest for exile as such Trikuta also went to forests. Meanwhile, Lord Rama, during his fourteen years of exile happened to visit Vaishnavi who recognized him immediately as no ordinary being but the incarnation of Lord Vishnu, and immediately asked him to merge her into himself so that she could become one with the supreme creator.
However Lord Rama, knowing that it was not the appropriate time, dissuaded her by saying that he would visit her again after the end of his exile, and at that time if she succeeded in recognizing him, he would fulfill her wish. True to his words, Rama visited her again after being victorious in the battle, but this time he did so in the disguise of an old man. Unfortunately, Vaishnavi was unable to recognize him this time and was distraught. Upon this, Lord Rama consoled her that the appropriate time for her being one with the creator had not come, and that time would come eventually in 'Kaliyug' when He (Rama) would be in his incarnation of 'Kalki'. Rama also directed her to meditate, and set up an Ashram at the base of Trikuta hills, to elevate her level of spirituality so as to bless mankind and rid the poor and destitute of their sufferings. Only then would 'Vishnu' merge her into himself. Vaishnavi, immediately set off for the northern part and after immense hardships, reached the foot of the Trikuta Hills. After reaching there she set up her ashram there and began to meditate.