Tanni was born on 26th July 1969 in Cardiff, Wales and Christened 'Carys Davina'. She was first called the name Tanni by her two-year-old sister Sian who, on first seeing her, declared she was 'tiny.'
As a young child Tanni wore callipers, she started to use a wheelchair from the age of seven. From the outset, her parents were supportive and encouraged her independent streak. Tanni's first school experience was at Birch Grove Primary, she is remembered there as a very determined young lady. Tanni tried many sports at primary school and particularly enjoyed swimming, archery and horse riding.
Tanni first tried wheelchair racing at St. Cyres Comprehensive School, aged 13. At 15 she won the 100 metres at the Junior National Wheelchair Games. At 18, Tanni became a member of the Bridgend Athletics Club, the British Wheelchair Racing Squad and was selected for her first World Wheelchair Games.