A 45-year-old woman is brought to the clinic by adult protective services after neighbors reported concerns about her 72-year-old mother, with whom she has lived exclusively for the past 8 years. The patient has no prior psychiatric history and was previously employed and socially active until she moved in to care for her mother following her father's death. Her mother has a long-standing diagnosis of delusional disorder, persecutory type, with fixed beliefs that government agents have placed surveillance equipment throughout the neighborhood. The patient now reports with apparent conviction that she has personally observed the surveillance equipment and has helped her mother cover the windows with aluminum foil. She describes elaborate precautions they take together, such as communicating only in whispered code and never using electronic devices. Physical examination and cognitive screening are unremarkable. When interviewed separately from her mother, the patient becomes slightly less certain about the surveillance but still maintains the beliefs are likely true. Which of the following best describes this clinical presentation?