Gina,
Next time or in the mean time get a copy of the subjects civil code as it pertains to the zoning issue in question. Here in San Diego the municipal code allows for a SFR to have 1.) an " Guest quarters " no kitchen, attached or detached, not to exceed 20% of primary residence GLA, or 2.) a "Companion Unit" AKA in-Law, Granny Flat etc.. Can Have a kitchen, attached or detached etc.....
When I encounter this problem I just site the appropriate Chapter, Article and Division of the code that allows the use. It ends all discussion on the matter. Here in San Diego we hav all sorts of allowable structures under a "conditional use" permit everything from border & lodger accomodations, employee housing, Home office/occupations, Fraternity houses, etc... so alot of my reports are subject to the owner providing a conditional use permit for the additional amenity. Our civil code is available on-line.
Good Luck.