Gemma was born in Tuscany. Her mother died when she was eight and her father when she was nineteen. She had suffered poor health from childhood, with a number of ailments including TB. Her health prevented her from joining the Passionist Sisters, which was her chief desire in life.

She left 230 letters to her spiritual director and her confessor, which revealed a humble and devout young woman willing to suffer anything in imitation of the passion of Christ and constantly aware of the presence of God.

She experienced rare experiences of God, the origins of which have been controversial. Some say she was possessed, some say her experiences were genuine. But when she was canonized in 1940 her letters were published, enabling a wider public to appreciate her good humour and commonse sense along with her great love of God.