We don't know for certain. However, in the Ju-Ni translation of chapter 416, Aizen says that he carved out the soul from hundreds of Shinigami and residents of Rukongai with Shinigami potential. We know that when Yammy used Gonzui, he sucked out the soul completely and thus killed, many ordinary residents of Karakura Town. However, Tatsuki, who has spiritual power enough to see ghosts and hollows, was not killed, just very weakened. Plus, Orihime and Chad, who have a lot of spirit power wasn't effected at all. So, in the case of Rangiku, Aizen could have performed a Yammy-gonzui deal and as a result Gin found her collapsed on the ground, much like Chad and Orihime found Tatsuki. But we don't know for certain and we really do have to wait to learn more.