Lammert's first international medal came at the 2003 European Athletics Junior Championships, where she won the bronze medal. She came fifth at the 2005 European Athletics Indoor Championships, won the shot put title at the 2005 European Athletics U23 Championships, and went on to represent her country at the 2005 World Championships in Athletics later that year. In 2006, she was the German Champion in the shot put both indoors and out and won her event at the 2006 European Cup. She was fourth at the 2006 IAAF World Indoor Championships and won her first major senior medal at the 2006 European Athletics Championships, taking the bronze with a throw of 19.17 metres.