Put your foot down. You're an adult and have legally rented the apartment. Tenancy laws and society bye-laws don't promote any kind of discrimination on the basis of gender, caste, religion or marital status. This is nothing but moral policing and harassment. The secretary is clearly crossing the line. Living peacefully is your right and this is just meddling. Talk to the owner or broker and tell him/her that the secretary is crossing her limits and that you won't tolerate this gross invasion of privacy. You're not breaking any laws. You can press charges against the secretary in the local police station.

Ask the landlord to ask the secretary to mind her own business and that you won't tolerate such nonsense. Bringing your date over is not illegal and it won't stand in the court of law.