There is a common story in almost all Puranas that Sita is Ayonija that is she is unborn and was there in the earth for several yugas or yeons. Parabrahman is omnipotent, Omni present, and omniscient. Sita, Maya, is the part and parcel of Parabrahman. Positive or negative energy, it is within us only. It is akin to this. Maya is negative energy. Energy can neither neither be created nor can be destroyed. One form of energy can be converted into another form of energy. This is called transducing. Parabrahman, the potential energy, is called Swayambhoo, the one that is self created. He is not created by anyone but he is source of creation. Maya, Sita, is the part and parcel of Parabrahman. As such Sita is also self born or Ayonija. She was not created.