In her welcome address at the Indira Gandhi centenary lecture, she said she learnt from her about India, its culture and values, as also her earliest political lessons.
"Her sacrifice in preserving a united, diverse, egalitarian India will be remembered. All the more so at a time when, in the quest for shortcuts to greatness, we find leaders willing to undermine the very foundations of our national character," she said.
"She saw an India that would not follow blindly the path laid by the West. She saw it crafting its own future guided by its democratic and cultural ideals. Where others failed, she wanted India to show the world the way. It made her mission doubly challenging, but Indira Gandhi was not a woman daunted by challenge.
"When Indira Gandhi spoke, she spoke for all Indians, men and women of all religions, regions, and backgrounds. No language was a barrier. She celebrated our magnificent diversity, battling those forces that foster division and strife among our people," she said.
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She also said that few have been called upon to make the supreme sacrifice in the cause for which they have lived and Indira Gandhi did so.
"Today we remember her life as one of leadership, courage and sacrifice. On this auspicious occasion, I bow my head in her memory," she said.
"She was an institution- a leader with the courage of her convictions and nerves of steel, unflinching in the face of duty, resolute against all that was unjust. She led our nation through the tumultuous battles of the 60s and 70s, never faltering in her dedication to the masses who gave her their complete trust.
"She faced economic crises, and prevailed. She managed the greatest refugee crisis in human history. She refused to compromise on India's noble humanitarian traditions. She faced war with courage and determination, and her victory saw the triumph of democracy and the liberation of a nation, Bangladesh," she said.
Gandhi's 99th birth anniversary, that marks the beginning of her birth centenary celebrations, and said that few Indian statesmen are now alive who could claim to have worked as closely with Indiraji, as the distinguished President.
She said Indira Gandhi was not a figure of history for her and being her mother-in-law who lived under the same roof, she shared joys and sorrows.
"It is from her that I learned about India, its culture, its values. It is from her that I imbibed my earliest political lessons. She was the Prime Minister of India, but to me she was a mother, a mentor, a friend. It was in my arms that she drew her last breath," she said.
"To her this idea was not a philosophical proposition laid down by her father, but a living experience as she travelled the length and breadth of this country, listening to the hearts of its men and women and giving them a voice.
Sonia recalled that it was this sense of duty that guided Indira in her mission as she sought neither personal glory nor wealth and every ounce of her energy was channelled in the service of her nation.
Among others present at the lecture by Mukherjee included former Prime Minister Manmohan Singh, Congress vice president Rahul Gandhi, Ghulam Nabi Azad, Anand Sharma, Sheila Dikshit and Mani Shankar Aiyar.