But retiring 18 years ago has not knocked the fight out of this woman, who is now committed to helping others, particularly disabled children, to enjoy sport and fitness as much as she has.
Over five Paralympic Games, the wheelchair racer, who has spina bifida, won 16 medals, including 11 gold, as well as winning 13 World Championship medals, holding more than 30 world records and winning the London Marathon six times.
Since retiring in 2007, Tanni has diverted her tenacity and determination to interests other than competing, including supporting Variety's Voices for Change campaign, which will work with children and young people across the UK to spotlight the challenges faced by disabled and disadvantaged children in accessing sports.
"I think disability still just gets forgotten," she said. "It's not a game of Top Trumps, it's not one protected characteristic over the other. It's about how we think we're inclusive to everyone in society."
Voices for Change says research shows disabled children from low-income families face a multitude of barriers to sports participation - including the cost of specialised equipment, which can cost up to 100 times more than standard kit, limited accessible facilities, transport problems and a shortage of trained coaches with expertise in adaptive sports.
"We need disabled children to have better access to sports, whether that's through the right equipment, training or getting to and from activities," said Tanni. "Not every child will become a Paralympian but every child should have the chance to try out sports - and even fail."
Does she feel optimistic about getting more disabled children active?
She said: "I think it's something we need to take seriously - it's about being fit and healthy, it's keeping people out of the NHS."
Although...