Does the questioner bear the sin of whoever misuses social media due to her encouragement of its use, or the sin of whoever reads a book containing incorrect ideas after it has been advertised in a reading club?

The mere suspicion of potential harm does not prohibit using Instagram to promote beneficial content, because the default ruling is permissibility, and the harm is only potential and could occur through other means. However, it is not permissible to choose a book that contains violations of Islamic law, due to the assistance in sin and causation of evil therein. Indeed, Allah Almighty records deeds and their consequences. "Whoever introduces a good practice will have its reward and the reward of those who act upon it, and whoever introduces a bad practice will bear its burden and the burden of those who act upon it."