Kira has very black and white thinking and her character arc is often about learning to see that life is more complicated than that even, or especially, during war.
Her mother was ultimately a survivor using whatever tools she had for taking care of her family which included taking care of herself. If she had let her position as Dukat's sex slave psychologically and emotionally destroy her he would have lost interest in her and discarded her. Her children would no longer be fed. So by embracing the role and enjoying aspects of it (good food, physical safety, conversation) she kept this arrangement, and therefore her children, alive. This is not weakness.