Final answer:
The most likely diagnosis for the client who believes the man she met briefly loves her and will marry her, despite evidence to the contrary, is Delusional disorder — erotomanic type.
Step-by-step explanation:
The most probable psychiatric diagnosis for the client who has been stalking a man she met briefly 3 years ago, believing he loves her and will marry her, is Delusional disorder — erotomanic type.
Delusional disorder, erotomanic type, is characterized by the false belief that another person, often of higher status, is in love with the individual. This delusion persists despite evidence to the contrary and is not due to the effects of a substance or another medical or psychological condition. The behaviors described, such as violating a restraining order and sending cards and gifts, are in line with the actions of someone who has this type of delusional disorder.