When Japanese troops invaded Penang in 1941, Puan Noor Aishah left primary school and learnt instead to cook and sew to supplement her family's income.

She peddled nasi lemak with her mother, took orders for embroidery and tried to pick up new skills, hungry to make up for the abrupt end to her formal education. This eagerness to learn put her in good stead when her husband Yusof Ishak was made Yang di-Pertuan Negara in 1959. Puan Noor Aishah was just 26.

Her role as spouse of Singapore's head of state put her in completely uncharted waters, she recalls in a new 200-page biography published by Straits Times Press and launched at The Arts House by Prime Minister Lee Hsien Loong yesterday.

Written by legal scholar and historian Kevin Y.L. Tan, the book also contains photos of Puan Noor Aishah and her family, including those from her private albums.

She said of her rapid adjustment: "I was not given any instructions or briefing at all; no guidelines. I had no task lists and no one briefed me on things like etiquette, dress codes and protocol. We had to learn and manage on our own."

She made her mark. She figured out the Istana's workings, and soon breathed new life into it by teaching its cooks - who were still preparing English classics like roast beef and Yorkshire pudding - her own recipes for local favourites like beef rendang.

She went for English lessons, organised events for dignitaries and became involved with voluntary organisations. And when her husband's health began to decline after a heart attack in 1968, she shouldered some of his social responsibilities.

PM Lee, who grew up playing with her three children, said of the book: "It will record for generations of Singaporeans her life story, the role she played and her contributions to our early nation-building days."

Since her husband died in 1970 of heart failure, Puan Noor Aishah, now 84, has largely kept out of the limelight, and the book offers a precious glimpse into her eventful life.

Born in 1933, she was adopted by Fatimah Ali and Mohammad Salim Jusoh, who was formerly known as Barney Perkins and had converted to Islam. They lived an unassuming life in Penang - until Puan Noor Aishah caught the eye of Mr Yusof. At 39, he was ready to settle down after years of rebuffing matchmaking attempts to focus on Utusan Melayu, the Malay daily he co-founded.

A close friend coaxed him into looking through photos of potential brides, and the last was of Puan Noor Aishah. Something about her face intrigued Mr Yusof, who told his friend: "This one, I agree."

He was whisked away to Penang for a first meeting. But, recalls Puan Noor Aishah, although her older sister took her to a garden one day to meet "a good man", all she did was sit at a table sipping tea. She never saw Mr Yusof, who was seated nearby so he could steal glances at her and was too shy to take a good look. Still, he wanted to marry her. They had their first proper meeting two days later, on their wedding day.

Puan Noor Aishah also shares details about her life with Mr Yusof: His favourite dish was rendang kerang (cockles rendang), and his pet name for her was "Teh", short for "Cik Puteh" (fair-skinned lady).

Their first home was in a small kampung with no running water or electricity. But these were tumultuous times for Singapore, and Puan Noor Aishah and Mr Yusof would soon find their lives upended.

When the People's Action Party won the 1959 General Election, Mr Yusof was first prime minister Lee Kuan Yew's pick for Yang di-Pertuan Negara. PM Lee noted Mr Lee wanted a distinguished Malay as the first head of state, to show the federation that Singaporeans accepted Malays as their leaders, and to forge good relations with Tunku Abdul Rahman and other Malay leaders.

PM Lee said Mr Yusof answered the call of duty, continuing as first president on independence, and discharged his duties with dedication and dignity while standing for the enduring values that underpin Singapore's success - meritocracy, multiracialism and modernisation - with Puan Noor Aishah by his side.

She insisted on living simply so their children's lives were as "normal" as possible. They lived in a small bungalow on the Istana grounds, and Mr Yusof paid the rent out of his salary. And while the family would lunch at the dining table using porcelain crockery and cutlery, they would roll out a carpet for dinner, and sit on the floor eating with their fingers, in the traditional way.

As the president's wife, Puan Noor Aishah kept traditions alive, from putting Malay dishes and kuih on the Istana menu to wearing kebaya - which she sewed herself - at state events. She transformed the tenor and feel of the Istana. In the colonial era, it was a "staid, stuffy, officious and distant place", the book notes, but by the end of 1960, it was "elegant, traditional, Asian, full of charm, warm and welcoming".

Puan Noor Aishah, who was at the launch with family members, including daughter Zuriana and granddaughter Fatimah Imran, said she was grateful for the effort behind the book. She was initially reluctant to have it, but friend and long-time neighbour T.P.B. Menon persuaded her to share her "unique and extraordinary" life story.

• Puan Noor Aishah: Singapore's First Lady costs $25 (before GST) at major bookstores.