Some versions of the Ramayana suggest that Sita was a reincarnation of Vedavati (an avatar of Mother Laxmi), an orphan lady. The legend goes thus:
Sage Kushadhwaja was a learned and pious scholar residing in a remote hermitage. His daughter Vedavati grows up in her father’s hermitage to become an ardent devotee of Vishnu, and resolves early in life to wed no one other than Vishnu. Her father refrains from stifling her aspirations, and even rejects proposals from many powerful kings and celestial beings who seek his daughter’s hand in marriage. Among those rejected is Sambhu, a powerful Daitya king. Smarting under his humiliation, Shambhu seizes an opportunity and murders Vedavati’s parents on a moonless night.
Vedavati continues to reside at the hermitage of her parents, meditating upon Vishnu. She is described as being inexpressibly beautiful, dressed in the hide of a black antelope, her hair matted, the bloom of her youth enhanced by her austerities. Ravana, the ruler of Lanka, once finds Vedavati seated in meditation and is captivated by her beauty. He propositions her and is rejected. Ravana mocks her austerities and her devotion to Vishnu; finding himself firmly rejected at every turn, he tries to molest Vedavati, pulling her hair. This greatly incensed her, and she forthwith cut off her hair, and said she would enter into the fire before his eyes, adding, “Since I have been insulted in the forest by thee who art wicked-hearted, I shall be born again for thy destruction.” So she entered the blazing fire, and celestial flowers fell all around. It was she who was born again as Sita, and was the moving cause of Ravana’s death, though Rama was the agent.
Her chastity thus sullied beyond redemption, Kedar immolates herself on a pyre, vowing to return in another age and be the cause of Ravana’s destruction. She is duly reborn as Sita, wife of Rama, and became the direct cause of Ravana’s destruction at his hands. In the process, Vedavati also receives the boon she so single-mindedly sought: Vishnu, in his avatara as Rama, becomes her husband. In some versions of the Ramayana, sage Agastya relates this entire story to Rama.
Valmiki wrote “The Ramayana”, an ancient Sanskrit epic thought to have been compiled between approximately 400 BCE and 200 CE “The Ramayana” does not mention Sita as Ravana’s daughter. However, the other versions of Ramayana started recreating stories telling Sita as daughter of Ravana and have their own explanation of why Sita was Ravana’s daughter.