The former Scotland star McAllister gave up his job as player-manager of Coventry City in 2003 to nurse his wife during her illness.
Denise's condition had been thought to be improving, but took a turn for the worse over recent months, according to the spokesman. She was in her late 30s.
The former Liverpool midfielder, 41, had said of his choice to quit Coventry to care for Denise: "As far as I was concerned it wasn't a decision. It was just the natural thing to do; I didn't want to be at a football club."
Denise was an ambassador for Breast Cancer Care and took part in a star-studded charity fashion show in 2002.