Lu Qing, the wife of the dissident artist Ai Weiwei, was questioned by the Beijing police for more than three hours on Tuesday afternoon, said an assistant who was with her. The officers asked Ms. Lu about her company, Beijing Fake Cultural Development Ltd.; personal details; and a housing project the company designed in Inner Mongolia several years ago. On a police form, Ms. Lu was listed as a suspect rather than a witness, the assistant said. She was told not to leave Beijing. Mr. Ai, a frequent critic of the Communist Party, was detained for 81 days this year and faces charges of tax evasion.