SONG CYCLE: Designer Brian Reyes’ after party is more like an afternoon tea since it’s from 12:30 p.m. to 2:30 p.m. following his show on Thursday. But those who attend the fete, hosted by Poppy Delevigne and Lauren Remington Platt as well as Gilt Groupe, will be treated to a midday surprise: a performance by Niia. The young singer and pianist, a Massachusetts native who trained as a classical musician, was discovered by Wyclef Jean. She sings on his single “Sweetest Girl (Dollar Bill)” and her mentor will be in the audience on Thursday to cheer his protégé along. Also there will be longtime Reyes fan Rachel Bilson.