It has taken nearly a century, but Australia is to get its first saint at last: Mary MacKillop, a 19th-century nun who spent her life helping impoverished children, and whose rebellious streak saw her briefly excommunicated from the Catholic church.

A teacher and social reformer, MacKillop founded a religious order at 24, and by the time of her death led 750 nuns who ran 117 schools, as well as orphanages, clinics and refuges for the needy. The work of her order, the Sisters of St Joseph, now extends to Thailand, Peru and Uganda.

Her canonisation had been widely anticipated after the Vatican credited her with a second miracle last December: the healing in 1993 of Kathleen Evans (66), who had been diagnosed with incurable lung and brain cancer. The first, declared in 1961, involved the curing of a woman with terminal leukaemia, who, like Evans, had prayed to MacKillop.

After a meeting of cardinals at the Vatican this weekend, Pope Benedict XVI ann­ounced that she would be canonised on 17 October. The news was welcomed by members of her order, and by Australians, some of whom prayed at her tomb in Sydney.

MacKillop's pioneering work included setting up schools in remote inland areas, educating women and helping the poor and the destitute. Her congregation broke with tradition by drawing its members from the working classes, allowing its nuns to move around openly in public places, and refusing to allow local priests to manage its affairs.

Her clashes with the church, and her egalitarian approach to her work, have led to her being called the "people's saint". She challenged orthodox thinking within the male-dominated church, and in 1871 was excomm­unicated for four months for insubordination.

Nowadays MacKillop – credited with helping to spread Catholicism in Australia and New Zealand – has a Facebook page, and a nun, Sister Annette Arnold, posts tweets on her behalf.

Born in Melbourne to poor Scottish immigrants in 1842, MacKillop opened the first St Joseph's School in a disused stable in the town of Penola, in South Australia. She died in 1909 and was beatified by Pope John Paul II in 1995.

Evans said last month that she had prayed constantly to MacKillop and worn a relic containing a piece of her clothing after being told she had only months to live. Ten months later, doctors in­formed her that her tumours had disappeared. Her medical records, she said, were closely scrutinised: "There were quite a few that examined me, but I didn't have any treatment, so there was no explanation." Evans added: "I do believe in miracles."

After being exonerated of wrongdoing, MacKillop sought the approval of Pope Pius IX to continue with her work. The campaign to have her canonised began in 1926, with the first application made for her beatification in 1961.