She was named by Swimming World Magazine as European Swimmer of the Year in 1985 and 1987, but her achievements are regarded with suspicion due to the state-run systematic doping program run by East Germany.

In 1991, former East German swimming coach Michael Regner claimed that in the 1980s he had been instructed to distribute anabolic steroids to team swimmers, including Hörner.

[1] Hörner came to prominence when she set a world record in the 200 m breaststroke of 2:28.33 at Leipzig in qualifying for the East German team for the 1985 European Championships.

At the 1987 European Championships in Strasbourg, France, Hörner won both breaststroke events, claiming the 100 m breaststroke record from Gerasch in the process and also a gold medal in the 4×100 m medley relay, resulting in her second European Swimmer of the Year award.

She later combined with Kristin Otto, Birte Weigang and Katrin Meissner to win gold in the 4×100 m medley relay.