Melanie Leupolz put Germany ahead 1-0 in the 24th minute by heading in a corner kick.
The 29th-ranked Thai hung within a goal behind a brilliant performance from keeper Waraporn Boonsing. But the Germans finally made it 2-0 on Petermann's header in the 56th minute - a feat she repeated two minutes later.
Sara Daebritz later closed the scoring by tapping the ball into an open net.
Germany finished atop its group with a goal differential of plus-14.
ICC T20 World Cup Global Qualifiers: Ireland trounces Thailand
Hegerberg's 2 goals lift Norway past Ivory Coast 3-1
MONCTON, New Brunswick, June 16: Ada Hegerberg scored twice to secure Norway's berth in the knockout stage of the Women's World Cup with a 3-1 win over Ivory Coast on Monday.
Norway (2-1-0) moves on as the second team from Group B behind Germany, and it will play the second team from Group F on June 22.
Hegerberg scored the opening goal for Norway in the 6th minute, beating Ivory Coast goalkeeper Cynthia Djohore at the near post. Hegerberg added her second with a left-footed kick in the 62nd minute, and Solveig Gulbrandsen put Norway up 3-0 in the 67th minute.
Ange Nguessan scored the only goal for Ivory Coast (0-3), a booming right-footed blast from well outside the penalty box in the 71st minute.
