Final answer:
Amendment 4 is most directly relevant to Jenny's right to decline a search of her purse by a police officer.
Step-by-step explanation:
The most directly relevant constitutional amendment to Jenny's right to decline a search of her purse by a police officer is Amendment 4. The Fourth Amendment protects individuals from illegal searches and seizures of their property, including their personal belongings like a purse. It requires that law enforcement officers obtain a warrant based on probable cause before conducting a search, unless certain exceptions apply, such as the person giving consent to the search or the presence of exigent circumstances.