Answer: c) Schizotypal personality disorder.
Explanation:
Schizotypal personality disorder is the disorder related with mental and personality health in which a person tends to behave strangely, faces social anxiety, strange and distorted  thoughts etc.
According to the question,if Reggie has dull, non-social and humorless personality then it might be due to fear with social situation and persistence of strange thought.Thus, she might have schizotypal personality disorder
Other options are incorrect because narcissistic personality disorder ,antisocial personality disorder and borderline personality disorder are not the personality disorder .This,the correct option is option(c).