"So many gathered from all over the world & lit candles to commemorate #2004Tsunami," tweeted Petra, with a photo of herself carrying a candle. "Join us & #Light4Tsunami 2 please."
The event was an emotional one for Czech Republic-born Petra, who, as well as losing Simon to the tsunami suffered a number of internal injuries and a broke her pelvis.
Stranded, Petra was forced to hold onto a palm tree for eight hours until Thai locals helped to rescue her.
Petra and Simon were on the last day of their holiday in the Thai resort on Boxing Day 2004 when the ten-metre high tsunami wave hit the bungalow they were staying in.
Petra and Simon in March 2004
The couple were immediately separated in the water and Simon later drowned. His body was found a few months later.
Petra's mental attitude helped get her through the devastating situation.
"I always try to direct any negative or sad energy into bringing something positive," said Petra, who set up the Happy Hearts Fund in 2006, a charity that builds schools in areas that have been affected by natural disasters.