You must understand the past life story of Sita. In her earlier life the name of Sita was Vedavati. She was performing Tapas (penance) with the desire to marry Vishnu Murti.  One day Ravana had seen her wanted her to accompany him to Lanka. She rejected this. He caught hold of her plaited hair and pulled. Instantly she created yogic fire (pyre), ‘in my next birth I will marry Vishnu Murthi, come to Lanka and destroy your family. Whatever portion of the hair left in your hand as many as Rakshasas will be destroyed ‘so saying she immolated herself in the fire. Her hair remained in the hands of Ravana. The very Vedavati born as Sita went to Lanka. The other name of Sita was Vaidehi, meaning one without body attachment. There are many such subtle secrets in the story of Ramayana. (Sri Sathya Sai Vachanamrutham 2008 Telugu page 96-97- DD on  28.6.2008)