It is said that once, she had accompanied Dasharath to a war against a demon. During the war, when Dasharath was supposed to have been injured, she drove his chariot out of the battleground, nursed him and got him back on his feet, fit to fight the war. Some other versions say that during the war, the axle of the chariot’s wheel broke and lest the chariot break down and bring Dasharath on the ground; she is supposed to have used her finger for the axle till the battle was over. King Dasharath was very impressed by her heroism, and granted her two boons, which she kept for a better day.
It is said that every action that one takes has a bearing on ones upbringing or some event of the past (especially childhood) which has moulded him/her the way s/he is as an adult. It was no different in the case of Kaikeyi too.
Some versions also say that she did all this under the instructions of Ram himself! According to this version, Ram once confessed to Kaikeyi, that he was Lord Vishnu on earth and he needed to go to the forests to eliminate many a demon and Ravana as part of his duty on earth. For this, could she do something to help him? He also warned her of the implications, and the stigma that would be associated to her name for ages. Kaikeyi could not have said a ‘No’ as she was an ardent devotee of Lord Vishnu and a stigma on her name was a relatively small sacrifice to be made, to get to serve the Lord himself. It is said that after her death, Kaikeyi found a place at Vaikuntha, the abode of Lord Vishnu.
Yet another version says that Kaikeyi’s father had overheard from some birds that the jungles would soon be full of demons that would hurt the Brahmins and ascetics, which would need a long-term helping hand of Rama. To ensure that Rama spent a lot of time in the jungles, and being aware of Manthara’s character, he ensured that she accompany Kaikeyi, after the wedding. He had full faith in her capabilities, and needless to say that she did live-up to the King’s expectations!