Lannaman was born in Aston, Birmingham, England and competed in her first Olympics in 1972 (held in Munich), where she set a British junior record of 11.45 sec.

In 1976, Lannaman won a silver medal at 60 metres at the European Indoor Athletics Championships in Munich.

She was strongly tipped for medals in both sprints at the 1976 Montreal Olympics, but due to injury was unable to compete.

She also ran the fastest ever electronically timed 100 m by a British woman with 10.93 sec in Dublin, which was wind assisted (+3.8), so did not stand for record purposes.

She competed again for Great Britain in the 1980 Summer Olympics held in Moscow, Russia in the 4 × 100 m relay, where she won the bronze medal with her teammates Heather Hunte, Kathy Smallwood-Cook and Beverley Goddard.