what makes dede realize they are living in a police state?

I'm not exactly sure where in Chapter 5 you mean but I'm thinking it begins when Lio and Jaimito both begin to come to the Mirabal house more and more. When Maria Teresa accidentally reads aloud to Mama a newspaper article that reveals that Lio is "a communist, a subversive," Mama becomes upset that she has been letting him spend time at their home. But Minerva continues to see him on double dates with Jaimito and Dede. Still, Minerva refuses to admit that she is in love with Lio.