Wearing a bright teal blue dress by Jason Wu--who designed her inauguration gown--and a sweater by Junya Watanabe , Mrs. Obama posed for photographs with Sarah Brown , Therese Rein , wife of Australian Prime Minister Kevin Rudd , Japanese Prime Minister Taro Aso 's wife Chikako Aso , and Laureen Harper , who is married to Canadian Prime Minister Stephen Harper , on the stage of the opera house .