Final answer:
The historical texts provided do not specify who helped Diana escape after Tiberius died, and without more specific information, it is impossible to answer with certainty.
Step-by-step explanation:
The person who helped Diana escape after Tiberius died is not explicitly mentioned in the historical excerpts provided. However, the texts do discuss various figures and events surrounding the reign of Tiberius, such as the death of Germanicus, the actions of Piso, the self-exile of notable individuals like Cornelia, and the accusations of witchcraft associated with the elite in Roman society. It's important to note that in the history of the Roman Empire, intricate plots and power struggles were common, and assistance could come from various sources, including political allies, family members, or even friendly factions within the Roman elite. Without a direct reference to Diana and her escape, we cannot determine who assisted her with confidence.