Still in the junior ranks in the 1987 season, she established herself at senior level. She won her first national title in the 800 m at the Czechoslovak Indoor Athletics Championships. This gained her selection for the 1987 European Athletics Indoor Championships and she made her first senior final, coming fourth and being beaten to a medal by Soviet runner Lyubov Kiryukhina. She also made the 800 m final at the World Indoor Championships held shortly after and a new indoor personal best of 2:01.85 minutes was a European junior record. It was also enough for a silver medal behind Christine Wachtel of East Germany. She was the first Czechoslovak woman to win a medal at the competition – only Ivana Kubešová joined her in that feat before the country's dissolution. Sedláková's European junior record lasted almost twenty-seven years before being improved by Iceland's Aníta Hinriksdóttir in 2014.