The Secretary was an affair of Van Coon, so why he simply didn't told the chinese gang where the hair needle is as they threatened him with a gun? I dont think he wouldn't sacrifice his life for her. She told Sherlock that he was not really attentive and it seems he wasn't realy in love with her. And it seems that she was in a very degrading situation. So maybe she was the one who stole the hair needle and he didn't recognise it because it was an inconspicuous thing.