Cho was always on the good side. She was one of the only people who believed Harry and Dumbledore that Voldemort had returned, even when the rest of the wizarding world, including many of the students, were ridiculing them for it. Cho's involvement in Dumbledore's Army, along with her willingness to return to Hogwarts to fight Voldemort and his Death Eaters, shows that she wanted to fight for the good side. This may be motivated by the loss of Cedric, or she may have been involved anyway.