On the twenty-first of March 1929 the million-selling Daily Sketch published a story on its front page about a popular young artist. An accompanying photograph showed a large framed oil painting being loaded on to a car. The backdrop was Sennen Beach.

Joan Manning Sanders' latest work of art was beginning its long journey from West Cornwall to the Royal Academy, where the capital's art elite eagerly awaited its arrival.

With her striking auburn hair in pigtails, and wearing a tartan skirt and knitted jumper, she could hardly look less bohemian. Yet by the late-1920s Joan had achieved worldwide celebrity status. At just 16 years old, she was the youngest person ever to have been accepted by the RA – a record that stands to this day. This young Cornish girl was photographed and feted, attended soirees at the Savoy Hotel and was written about by all of the most influential art critics of the day.

But why, you may ask, does her name not appear alongside other doyen of Cornwall's Edwardian art scene: Forbes, Harvey, Langley, Proctor, Knight? All is revealed this week with the opening of an exhibition at Penlee House Museum and Gallery in Penzance. A Forgotten Prodigy: Joan Manning Sanders is the first airing of the artist's remarkable talent since the 1930s.

So who was she and why did she disappear so completely from the art radar? Was it a tragic early death? A fall from grace? Insanity? Her biographer, Owen Baker, takes up the story. A former county librarian for Devon, Mr Baker had long been fascinated by what has become known as the Newlyn School of painters. He was intrigued by occasional dead-end book references to "child prodigy Joan Manning Sanders" but never followed them up. Then one day in 2002, while at home in Penzance, he opened his copy of the Western Morning News and, to his surprise, saw a half-page obituary.

"It was written by Frank Ruhrmund," said Mr Baker. "And as well as the completely unexpected discovery that she had been still living in Penzance all this time, there was information about her early life as a painter. It was clear Joan had been what we would now call a celebrity."

Reading the obituary to the end, Mr Baker was even more surprised to learn that John Floyd, a bibliophile and secondhand book dealer with whom he had been acquainted for some years, was Joan's son.

"I just couldn't believe it," said Mr Baker. "This international celebrity from the 1920s had been living quietly in Penzance for all those years."

Fired by this knowledge, he spoke to John Floyd and, as a supporter of Penlee House, set about organising a retrospective exhibition of her work. However, even with the full support of gallery director Alison Bevan, it proved to be an extremely difficult task. Despite there being a comprehensive and illustrated catalogue of her work, compiled in the early 1930s, no one knew the whereabouts of the extensive collection of canvases.

Joan's son was able to help with a few, but even these presented problems. Taken out of their frames or off stretchers and rolled up by the artist many years before, they had lain untouched and deteriorating. Fortunately, the conservation department at the Courtauld Institute in London offered to work on three of these, while Penzance conservator Alison Smith tackled a further two. Appeals also went out locally and through art networks, asking if anyone knew the whereabouts of Joan's lost paintings. But to no avail.

"You can see why it has taken so many years to put the exhibition on," said Mr Baker. "And why there are only eleven paintings on display."

There may only be 11 works at Penlee, but their impact is no less than if there were 50. What's more, Alison Bevan and her team have hung two adjoining rooms with works by artists associated with Joan. Among them are paintings by Annie Walke and Ernest Proctor and two by Joan's father, George. Alethea Garstin, Lamorna Birch and Midge Bruford are also represented. By standing in a particular spot and viewing Laura Knight's Blue And Gold to the left, Dod Proctor's Little Sister to the right and Joan Manning Sanders' St Anthony With Pigs through the middle, it's easy to see where the latter's influences lay.

"Joan was lucky in many ways because she had access to some of the finest painters of the age," said Alison. "Her parents were bohemians, living in a gypsy caravan. George was a writer and painter and Ruth was an extremely successful author. Joan knew the Proctors, the Harveys, the Walkes and the Knights and it seems they took her under their collective wing and encouraged her talent."

Joan's career was truly remarkable. Born in 1913 and raised surrounded by the celebrated Newlyn School artists, it is perhaps unsurprising that an early glimpse of artistic talent was nurtured. She received her first commission from Father Bernard Walke of St Hilary when she was only 13 and the six paintings she produced remain on view in the church's Lady Chapel.

By the age of 16, she had exhibited several times in London, her work being selected for the Royal Academy summer exhibition. Two hardback books were published about her work, one in the UK and one for the American market. This, together with widespread media coverage, made her a household name.

So what happened then and why was she forgotten? It seems that it was a clear case of falling out of fashion. Joan was working at the tail-end of a movement which valued empathic figurative representations in naturalistic settings. But despite several attempts at modernism, Joan's heart simply wasn't in it.

"Consequently, paintings that had caused a sensation when first exhibited were consigned to the attic, taken off their stretchers and rolled up to save space," said Alison. "Works once purchased for substantial sums by enthusiastic collectors have vanished from record and cannot be traced. The shining star of Joan the child prodigy vanished from our vision.

"However, due largely to Owen's enthusiasm, we now have 11 of her works on show. Owen and I agreed that she had been too long in the wilderness and that her work had to be seen again. This story has been sitting in Penzance, unnoticed, for all these years, so it is a privilege to bring it to a wider public.

"But there must be many more of Joan's surviving paintings out there and we would love to hear from anyone with information about any of her lost works."