The Gift, a pounds 1m-film, recounts the experiences of a young mother, ravaged by cancer, who faces the prospect of leaving behind a seven-year-old child.
Ms Gannon, 48, was herself only six when brain cancer claimed her mother and left her father, a soldier, to bring up three children.
The writer, a housewife in Derbyshire before she took to scripting nine years ago, said: "The project is very important to me.
"When my mother died I was much the same age as the little girl in The Gift. The girl in the film has good memories of her mother, memories that I did not have even though I grew up knowing I was loved, which is the greatest gift a mother can give her child."
The Gift will star Amanda Burton, who teamed up with Ms Gannon on the set of Peak Practice. Neil Dudgeon, Trevor Peacock and Crispin Bonham- Carter, who appeared in Pride and Prejudice, will also star in the film.