Rebecca F John, a 28-year-old Welsh ski instructor who is training to be a teacher, has made it on to the shortlist for the Sunday Times’ £30,000 short story prize ahead of major names such as Mark Haddon, David Peace and Joseph O’Neill.

John’s story, The Glove Maker’s Numbers, tells of a woman who is institutionalised when she is unable to cope after the death of her brother. It made the lineup for the Sunday Times EFG short story award – the world’s richest prize for a single short story – alongside works by five critically acclaimed writers, including Yiyun Li, whose A Sheltered Woman follows a Chinese-American nanny helping out a new mother and her baby, and Elizabeth McCracken, whose Hungry features a grandmother intent on fattening up her granddaughter.

Currently studying for a PGCE in post compulsory education and training, John is also a ski instructor and an English tutor – but said it has always been her “intention, or hope”, to write full time. Her first short-story collection, Clown’s Shoes, will be published by Welsh press Parthian this autumn.

“It is only over these last weeks, though, that this has begun to feel like a real possibility,” she said. “I still find it difficult to believe that I ended up sandwiched on the longlist between Mark Haddon and Yiyun Li – their books have been on my bookshelf for a long time. So to now be included on a shortlist with just five incredible writers ... It’s such a shock.”

The shortlist is completed with a third US author, Scott O’Connor, chosen for his story Interstellar Space, New Zealander Paula Morris’s False River, and Canadian Madeleine Thien’s The Wedding Cake.

John’s story, said the writer, details the attempts of a young woman, Christina, to recover after she is institutionalised “by creating an elaborate mental system of numbers via which she might order her life”.

“I was inspired to write the story after watching a documentary some time ago,” said John. “There was one woman’s story included in it which really moved me. This woman was a single mother, working numerous jobs to provide for her children, who, when she worked herself to exhaustion, was institutionalised and subsequently lost the children. I didn’t want to recreate that woman’s story exactly. I wanted rather to give her the happy, or hopeful, ending she was denied. That’s how Christina came into existence. She was my homage to that unknown woman.”

John hopes the shortlisting will help her work “find a much wider audience now than it would previously have done, and that’s all we want – isn’t it? – as writers: to find an audience; to have somebody listen to what we felt we had to say.”

The winner of the £30,000 award will be announced on 24 April, joining former winners including Junot Diaz, Adam Johnson and CK Stead. Running for six years, the Sunday Times prize has never been won by a woman, or by a British writer.

Alex Clark, on this year’s judging panel, said that the final six stories selected by judges “represent the variety, ambition and invention we encountered throughout the judging process – and they also reflect the continuing health and vitality of this wonderful form”. Clark is joined on the panel by the director Richard Eyre, the authors Elif Shafak and Aminatta Forna, Sunday Times literary editor Andrew Holgate, and non-voting chair Lord Matthew Evans.