She was born in Milan in 1907, the youngest of Toscanini's four children. Her own musical ambitions - as pianist and singer - were drowned by her father's intolerant perfectionism: she couldn't practise when he was within earshot, since "a mistake was like a stab in his stomach", and so she helped her mother look after the capricious, self-centred conductor.
This early training in the technique of coping with superstars came into its own when in 1933 she married Vladimir Horowitz, then 29 and well on the way to acquiring the label of "world's greatest pianist". She was instantly attracted to him, both physically and intellectually: "In the first place he was good-looking," she later recalled, "And his playing! I heard him play in a house after a concert . . . I remember I went home and said, `I never heard anyone play a mazurka of Chopin like this.' " They were married in the same year, and her 55-year-long career as minder of a deeply insecure musician had begun.
The relationship was not easy. Horowitz's homosexuality cannot have helped. Their only child, Sonia, was born early in the marriage and led a troubled life, not least because of the relative indifference of her father; she died at the age of 40 in 1974, as the result of injuries sustained in a motor-cycle accident.
It was hardly surprising that Horowitz and his wife separated in 1949 - but briefly, as it turned out. His lack of conviction in his own abilities - so unsettling that for 12 years this most gifted of pianists was certain he would never play again - needed the bulwark of her self-confidence. When Horowitz died, on 5 November 1989, Leonard Bernstein paid tribute to her "long years of devotion to this amazing man". Horowitz was, he said "not only a super-pianist but a super-musician with all the mental fallibilities such geniuses have. You cared for him and guarded him through a series of neurotic crises the world may never know nor understand; and you returned him to us time and again, refreshed, renewed and ever greater."
Indeed, Wanda Horowitz was the backbone her sensitive husband could not generate on his own. When he took to the piano again after his long silence, she packed his bags, examined the hotel rooms, supervised the food, screened telephone calls, argued with managers, stood firm against record companies, often using considerable musical judgement of her own.
That tough exterior was not simply a protective ploy: her scowl was legendary, and she inherited her father's temper. "My father made me neurotic and my husband made me crazy," she snapped at one reporter who asked about the two men in her life. But she summed up her own achievement with quiet satisfaction: "To be the daughter of Toscanini, I didn't have any merit because I could have been born to anybody. But to be the wife of Horowitz, in that I take a little bit of pride."
Wanda Giorgina Toscanini: born Milan, Italy 5 December 1907; married 1933 Vladimir Horowitz (died 1989; one daughter deceased); died New York 21 August 1998.