She was a member of Wolverhampton & Bilston Athletics Club, competing in both javelin and multi-event disciplines. In 1972, aged 16, Sanderson won the Intermediate javelin at the English Schools' Athletics Championships. The following year she was selected to compete in the javelin throw at the 1973 European Athletics Junior Championships, where she reached the final but finished 12th with , well behind the winner, Tonya Khristova, who threw . After this competition, Sanderson decided to focus on the javelin event rather than pentathlon, partly because she expected competing in the javelin to provide more opportunities for travel. She made her senior international debut in the javelin throw at the 1974 British Commonwealth Games, finishing fifth. Later that year, she finished 13th at the 1974 European Athletics Championships. Sanderson broke the UK javelin throw junior record five times, achieving in 1974. She became the national record holder in 1976, throwing . She went on to achieve ten new UK senior records and five Commonwealth records.