She rattles off the history of Methodism in this city, as well as tidbits about William T. Sherman’s March to the Sea. She discusses the canopy of Spanish moss that hangs above Savannah’s streets, whether “Jingle Bells” was actually composed here, and just how haunted one of the country’s largest historic landmark districts might be.

But Ms. Freenor has also emerged in recent weeks in a new role: plaintiff in a federal lawsuit that could reshape Savannah’s lucrative and potent tourism industry. Backed by a nonprofit law firm with libertarian leanings, Ms. Freenor and three others, including her husband, are challenging the Savannah ordinance that requires tour guides to hold licenses and pass regular academic and medical examinations.

“It’s the free market that made us successful, not the City of Savannah,” said Ms. Freenor, 43. “You shouldn’t have to pass a test to be able to tell people where the best ice cream in Savannah is.” She said autoimmune disorders could make her need a wheelchair in the coming years and keep her from receiving a compulsory doctor’s certification.

The case here is the latest significant courtroom pushback to municipal regulations that govern tour guides in a…