Kupfernagel captured the Emakumeen Bira cyclo-cross race three consecutive years from 1997 to 1999.
In 2007, the three-times world cyclo-cross champion added world time trial champion to her palmares when she won gold at the 2007 UCI Road World Championships Women's Time Trial.
She also won the Sparkassen Giro Bochum.
In 2008, she had a very strong cyclo-cross season, winning two [World Cup] races and even though she finished at second place for six times, she had enough point to claim the overall World Cup title.
She seemed to be the favourite for the women's race at the 2009 UCI Cyclo-cross World Championships in Hoogerheide, she was not able to defend her title as Marianne Vos beat her during a sprint finish and left her with the silver medal.