I have heard that Sita had come to see when lord Rama and Laxman were lying on the battle field after Indrajit stuck down them with Naga-phasha.
Did Sita come to see? and who has brought up her to the battle field?
As I discuss in this answer, Indrajit once fatally wounded Rama and Lakshmana using Nagastras or snake weapons. Rama and Lakshmana were ultimately rescued by Vishnu's bird Garuda, who ate all the snakes. But before that happened, Ravana, thinking that Rama and Lakshmana were dead, told Trijata and other Rakshasis to take her to the battlefield in the Pushpaka Vimanam, as described in this chapter of the Yuddha Kanda of the Ramayana:
Following his orders, the female-demons along with Trijata appeared before him. Then, the rejoiced Ravana said to them as follows: "Tell Seetha that Rama and Lakshmana have been killed by Indrajit. Take her in Pushpaka the aeroplane and show her Rama and Lakshmana who were killed in battle. Her husband, the one depending on whom rendered her so proud that she refused to be united with me, lies there killed with his brother in the battle-front. From now on, free from anxiety, grief and expectation of reunion, Seetha the princess of Mithila kingdom, adorned in all her jewels, will submit herself to me. Beholding Rama and Lakshmana fallen under the sway of death on the battle-field today, finding no other haven and hoping for nothing else, the large-eyed Seetha will voluntarily seek refuge with me!" Hearing these words of the cruel Ravana, they all replied, "Be it so" and went to where the Pushpaka chariot was. Thereafter, the female-demons brought the aerial car, Pushpaka as per the instructions of Ravana and carried it nearer to Seetha who was staying in Ashoka-grove. The female-demons brought Seetha who was afflicted with grief for her husband and made her to ascend Pushpaka-plane. The female-demons along with Trijata made Seetha to ascend Pushpaka-plane and proceeded to show her Rama and Lakshmana. Ravana the king of demons, thrilled with rapture, caused Lanka to be garlanded with flags and banners and arranged a proclamation to be made in Lanka announcing that Rama and Lakshmana had been slain by Indrajit in battle. Seetha along with Trijata, transported by that plane, saw all the monkey-troops who had been slain. Seetha saw the demons who were delighted at heart and monkeys disturbed with grief, standing round Rama and Lakshmana. Then, Seetha beheld those two warriors Rama and Lakshmana lying unconscious on the ground on a bed of arrows, their limbs pierced with arrows, riddled with weapons, their armour shattered, their bows cast aside at a distance and their entire body transfixed by darts. On seeing those two brothers, who were filled with valour, having lotus-eyes, the excellent of men, lying stretched on a bed of arrows there in that wretched plight like the two sons of the fire-god (Shakha and Vishakha) lying on a bed of reeds, Seetha wailed piteously, stricken as she was with a great agony. The dark-eyed Seetha the daughter of Janaka with her faultless limbs, beholding her lord and Lakshmana lying in the dust, burst into sobs. Witnessing those brothers, the prominent sons of god, Seetha afflicted with tearful sorrow, believing their death, spoke with grief the following words.
Sita was lamenting the apparent deaths of Rama and Lakshmana, but then Trijata reassured her that they were still alive, as described in this next chapter of the Yuddha Kanda:
O, the god-like lady! Do not despair. Your husband, Rama is still living. I will tell you mighty and cogent reasons, how these two brothers Rama and Lakshmana are living. The leader having been lost, the faces of the soldiers on the field of battle are never seized by anger nor are they animated with joy. O, Seetha! This aerial car called Pushpaka by name, celestial as it is, would not have brought you here, if those two heroes have lost their lives. An army that sees its valiant commander fall, is bereft of courage and wanders aimlessly about on the battle field, like a ship which has broken its rudder in water. This army for its part is neither confused nor perturbed and is guarding Rama and Lakshmana. I am pointing this out to you on account of my affection for you, O lady given to austerities! You as such, be reassured by these auspicious omens. Behold Rama and Lakshmana who are not dead. I am telling you this, on account of my affection for you. O, Seetha! I have not spoken falsehood before, nor shall I ever do so. By your conduct and natural gaiety, you have found a place in my heart! Even celestials and demons along with Indra cannot vanquish there two heroes in battle. This is what I have observed and communicated to you. O Seetha! See this, a great marvel! See how, fallen under those shafts and deprived of their senses, their beauty has not deserted them. Generally, the faces of those who lost their lives and whose vital power has vanished, will be appearing with an appalling alteration. O, Seetha! Banish your grief, pain and ignorance on account of Rama and Lakshmana. It is impossible, now with the splendour seen in their faces, for Rama and Lakshmana to die.
The reason that the army wasn't in disarray, by the way, is that Vibhishana reassured them that Rama and Lakshmana were still alive.