That Wonderful Urge (1948)

An investigative reporter uses a ruse to meet Sara Farley, a grocery-store heiress he's been writing unflattering things about. He gets her to start talking about herself and finds her down-to-earth and engaging. Before he can publish an honest and admiring story, she finds out who he is, assumes he's going to write more lies, and sets out to undercut him by announcing to the press that the two of them are married. In trying to get the truth out, he loses his job, the two of them spend time in jail, and the stakes escalate. Finally, he sues her for libel, and a court tries to set things right.