An 11 time Hungarian Athletics Championships winner in 400 metres, Petráhn matched the national record of the distance (51.50 seconds) in 2006, tying Ilona Pál's record set in 1980. She raced at two Olympics in this event in 2000 and 2008. In her first participation at the 2000 Summer Olympics in Sydney, Petráhn made it from the first round to the quarterfinals, where she came last in her heat and did not advance further. At the 2008 Summer Olympics in Beijing she came only fourth in her first round heat thus did not manage to go to the quarterfinals.