Thomas was vicar of St Michael's church Eglwysfach from 1954 to 1967
A Welsh language BBC Wales documentary will focus on an artist whose work was overshadowed by that of her husband, the poet RS Thomas.
O Flaen dy Lygaid also features calls by the couple's son, Gwydion to bring one of her greatest works back to Wales.
In a rare interview he gives a personal insight into this extraordinary creative partnership.
The programme is broadcast on S4C at 2100 GMT on Tuesday, 18 May.
Mildred Elsie Eldridge was a talented London artist, with successful one-woman shows and a Bentley in her drive.
She had been one of the brightest students at the Royal College of Art, winning the prestigious Prix de Rome which gave her access to Europe's most exclusive social circles.
But she turned her back on the glitzy London life when she accepted a post as an art teacher in Oswestry.
Here she met the man she would marry and for whom she would sacrifice her own ambitions - RS Thomas.
The programme looks at how Mildred Elsie Eldridge lived her life in the shadow of her husband's great talent.
He remembers his mother painting Life's Dance, a mural for Gobowen Hospital, at their home in Manafon, Montgomeryshire, and finishing it in Eglwys-fach, Ceredigion, where the family went to live before eventually moving to Aberdaron.
"I think it's on a par with the Whistler panels in London," said Gwydion Thomas of the painting.
"I think that somebody should shift themselves and find a building for it in Wales. It should be on show."
Art historian Peter Lord is seen viewing the 120 foot mural in storage.
"It's a masterpiece on so many levels," he said.
"But just on a technical level the concept of such a large, ambitious piece is amazing.
"What strikes one is the physical effort that went into it and the difficulty of working on this scale, without a suitable studio."
And RS Thomas scholar Jason Walford Davies throws new light on the symbiotic relationship between Elsie and RS, revealing the parallels in each other's work and how each influenced the other.
Mr Davies said: "The key to understanding Elsie's influence on RS is as a catalyst.
"She was the promoter, the one who made things possible, who helped realise his potential and made possible his dream of a poetic career."
The programme provides insight into a woman who was the force behind her family, and whose death prompted some of RS Thomas's most outstanding and powerful works.