Best bet: An honest cop, an informer or records from the prostitute scandal. Cops know who these hookers are, where they hang and who their pimps are. Durham is not unusual.
More likely Nifong had her hauled in and confronted with her lies about not having consensual sex with anyone within five days prior to the alleged incident, and threatened her with prosecution for obstruction and possible other charges if she didn't fess up.
The drivers would probably not admit to having sex with her unless she named them. Further, the defense apparently didn't know about the unidentified semen sample in her at the time they announced there was no DNA match to their clients.