Thank you for your question. I look forward to working with you to provide you the information you are seeking for educational purposes only.
Legally, if the municipality claims you have an illegal or unauthorized apartment, they have the right to investigate. The homeowner does not have to allow them on their property without a search warrant
, but if the homeowner does so, the director of the inspections division has the right and authority to issue an administrative search warrant to force you to allow them entry, so make your decision wisely as you can imagine they will not give you the benefit of any doubts on any questionable violations they may typically overlook for a cooperative homeowner. However, you have the absolute right to refuse any government entity entry onto your property or into your home without a search warrant as guaranteed by the 4th Amendment.
If your accessory apartment does not fit into the guidelines listed at http://www.brookhaven.org/DesktopModules/Bring2mind/DMX/Download.aspx?EntryId=229&Command=Core_Download&language=en-US&PortalId=0&TabId=1181
and it is not a rental or being rented out you need to provide them proof of those facts and they do have a right to verify that you are not violating the law by not having the required permits for the apartment. An accessory apartment is defined in Brookhaven as a small rental housing unit designed in particular to meet the special housing needs of single persons and couples of both low and moderate incomes, both young and old, and of relatives of families presently living in the town of Brookhaven. See: Brookhaven Code 85-411A.
So you have to prove it is not a rental unit, she is simply living with you there in exchange for no rent or fees or payment of bills for it to not be deemed an accessory apartment.