Is the act of slandering the Prophet's mother, which necessitates the death penalty for its perpetrator, confined to defamation and accusation of adultery, or does it also include the statement that she is among the people of Hellfire?

The "slander" (qadhf) mentioned here refers to accusing someone of indecency. This is supported by Ibn Qudamah's reasoning in Al-Mughni for this ruling: that slandering the Prophet's mother necessitates execution because it is an act of slander against the Prophet himself and an impugnment of his lineage. Therefore, whoever slanders the Prophet's mother is considered an apostate from Islam, and their punishment is execution.

The punishment for slandering the Messenger's mother (peace be upon him) has no relation to the matter of her fate in the Hereafter.