Lil Alexander, 70, said she was upset to learn the BBC programme had already started filming and she insisted she would have not allowed it to go ahead if producers had sought her permission.
Mr Alexander and his brother Tom performed for more than 50 years together as the Alexander Brothers and toured the world at the height of their fame, playing venues such as Carnegie Hall, New York, and Sydney Opera House.
Jack died in November, aged 77, after suffering a series of strokes.
Mrs Alexander said she found out about the documentary when a researcher called to ask for memorabilia to feature on the show.
She said: "Have they no soul or conscience to think how I feel about it? It's just so cold and calculating how they just step over everything.
"Jack's brother didn't even phone me to tell me it was being filmed, If he had done I would have said 'No, I'm sorry, I don't want anything done until at least eight to 10 months from now.'
"The film wouldn't have been made at all if it wasn't for Jack dying. They could have made the film last year when he was still alive, but they didn't.
"His death has left a hole in my heart."
Mrs Alexander, of Prestwick, and her husband were married when she was 40 after first meeting when she was a teenager and he was in his 20s.
A spokesman for the BBC said the programme would be a "fitting and affectionate" tribute to the musician.