Guru Gobind Singh’s greatest contribution was the establishment of a Sikh tradition, with its own distinct form and character and intellectual and spiritual alertness. The Khalsa faith revolutionized the ways of thinking and living of the common man. Ordinary people were turned into bold and fearless warriors, self-reliant and capable of independent thought.

After the death of Guru Gobind Singh, for the remaining 40 years of her life, Mata Sundari Ji took up all the tasks that had been initiated by the Guru and established herself as a capable successor and leader of the Panth.

An even greater task completed by Mata Sundari was the compilation of the works and writing of the tenth Guru into what is now known as the Dasam Granth. It was a formidable challenge to search for and locate all the scattered material, but Mata Sundari proved equal to the task. The tenth Guru was a scholar of Brij, Avadhi, Sanskrit, Arabic, Persian and Punjabi. He was also a translator from the Sanskrit. His own works are voluminous, written mostly in Brij Bhasha, the literary language of Northern India, but also in Punjabi. It weighed nine maunds, approximately 340 kg. The entire work was put together into on volume entitled Vidya Sagar. But this valuable piece of work was lost in the flooded Sirsa river during the march from Anandpur. But copies of the hymns had been prepared side-by-side with the original work and these were now in the possession of Sikhs scattered all over the country, who were using them to learn the hymns by heart and recite them in their daily prayers.

Under the supervision of Mata Sundari, Bhai Mani Singh undertook the task of collecting these pieces and compiling them into what came to be known as the Dasam Granth. The workers of the Takht Sri Harmaindir, Patna, cooperated whole heartedly and collected much material. This was compiled by the end of the 18th century and came to be known as Patna Di Missal. A large amount of money was donated by Kesar Singh Chhiber so that funds were not lacking for the use of Bhai Mani Singh in Amritsar. This was distributed in order to trace the poetical compositions of Guru Gobind Singh. The task was a daunting one, for the Guru’s Sikhs were scattered in faraway places. Some had sought shelter against the atrocities of the government in hills and forests. Some works had passed into alien hands, who refused to part with them unless given payment. By a stroke of good luck, Mata Sundari came across a list of works written by Guru and this list even contained his signature. This proved valuable in checking the material for the final volume.

Not only did Mata Sundari initiate the compilation of the sacred writing of Guru Gobind Singh, she also persuaded the Sikhs to prepare copies of the holy hymns of the Adi Granth. Bhai Mani Singh was also instructed to prepare such a volume. 

Extract from: 

http://www.searchsikhism.com/mata-sundari-a-multi-faceted-personality