There is not a specific moment in this novel in which Dede realises what Trujillo has done. Rather, she, just like all the other sisters, become gradually aware of the extent of Trujillo's despotism and they grow up in a country where every word has to be watched so carefully and where oppression is a natural part of life. What distinguishes Dede from the other sisters, however, is the way that she does not let the reality of Trujillo's dictatorship move her into opposing him, as is the case with Minerva, Patria and Maria Teresa. Instead, when her sisters try and persuade her to join them in opposing Trujillo, she hides behind her husband's cowardice in Chapter Nine, allowing her husband to dictate that they cannot store any munitions for the rebel movement in their land, and then even choosing not to join her sisters in their rebel cell when they come personally to try and encourage her to be part of what they are trying to achieve. Note what reason Dede gives for not joining this rebel movement:
"Jaimito thinks it's suicide. He's told me he'll have to leave me if I get mixed up in this thing." There, she had said it. Dede felt the hot flush of shame on her face. She was hiding behind her husband's fears, bringing down scorn on him instead of herself.
Dede therefore does not have a moment of specific realisation about the extent of Trujillo's crimes; rather, she, like her sisters, grow up gradually realising more and more about the evil nature of Trujillo's rule. The only difference with Dede is that this information does not tempt her to openly join the rebel movement.