Even after 100 years, the four seconds of blurred stuttering newsreel have the power to shock.

Slow it down and you can see the statuesque figure of Emily Wilding Davison duck beneath the barrier at Epsom's Tattenham Corner on Derby Day 1913. Briefly she raises her arms before being mowed down by Anmer, the King's horse. Her wide-brimmed hat flies off as she is catapulted on to her back, her skull smashed like an egg, though it took her four days to die.

Clare Balding's enthralling Channel 4 documentary to mark the centenary of the event set out to show that Davison planned a spectacular protest but not suicide. Perhaps it missed the point. Her return train ticket and the apparent attempt to pin the suffragette colours (purple, green and white) on the horse do support Balding's thesis but the fact remains that Davison was more than ready to die for her cause. In fact, she had attempted suicide in prison the previous year. A woman prepared to serve eight jail terms and withstand forced feeding 49 times in her desperation to win women the right to vote is prepared to do anything.

Her life moulded her radicalism. Forced to abandon university to support her widowed mother, she scrimped and eventually used the embryonic St Hugh's College Oxford to take First Class Honours in English, though could not graduate because the university did not award women degrees. In 1903 she joined the Women's Social and Political Union but even by their standards of militancy was regarded as something of a loose cannon. "Deeds not words", is not just her epitaph but also her epigram, even if her notion of direct action was sometimes misplaced, as when she attacked a Baptist minister in Aberdeen Station, having mistaken him for David Lloyd George.

The abandonment of the 1910 Conciliation Bill (extending the franchise to some women) and the violence of the police in the subsequent Black Friday demonstration must have been the last straw. To understand her desperation and dedication, it is important to appreciate the vilification directed at suffragists by the establishment and a misogynist press. The Glasgow Herald's bilious leader on June 5, 1913 was not untypical: "It is not possible to describe the mad act of this woman as anything but a paroxysm of sheer lunacy. Few would have felt the smallest regret if the early reports of her death had been correct and the sympathy of all sane people will be directed to the unfortunate jockey" (who escaped with mild concussion and a bruised arm). It goes on to dismiss the women's suffrage movement as "insincere trash". Yet the huge funerals in London and her native Northumberland demonstrated the depth of support for women's suffrage. Davison may have been an accidental martyr but she was a martyr nonetheless and, along with the social upheaval precipitated by the First World War, probably made universal suffrage a done deal by 1928.

Last month even Epsom racecourse marked her place at the barrier on Tattenham Corner with a discreet plaque. Later this year I will join other St Hugh's old girls to celebrate the tragically truncated life of Emily Davison. She would be delighted to hear that her alma mater went on to produce Barbara Castle and Theresa May, two of Britain's most outstanding politicians.

And if I haven't reached their giddy heights, at least she would be more approving of my leaders for The Herald pressing for a fairer deal for women in politics and the workplace, than the bile that spilled from my predecessor's typewriter as she lay dying in Epsom Cottage Hospital.

Surely, she would celebrate the progress women have made in education, business and sport and the extent to which today's fathers share more of the burdens of parenthood, even if she would observe that women in countries such as Saudi Arabia and Iran are still fighting her old battles. But undoubtedly her biggest disappointment would be that 100 years after her doomed Derby Day dash, fewer than 40% of women canvassed on the issue are sure they will vote in the next election. Deeds not words, girls. Our deed is to make sure we use the vote she died for.