Ms. Villarreal reports entirely on Facebook, often by live-streaming video on her page on her iPhone. Some follow her because of her fire-breathing reporting style, blending facts with chisme (gossip), but many in Laredo welcome her exposés on public corruption in a city whose abundant reports of graft are the target of an F.B.I. investigation.

In February, for instance, she scooped the competition with a report about a former Laredo police investigator who was accused of taking gambling proceeds from raids on slot-machine casinos, then was allowed to resign when confronted with the findings.

It took days for competitors to finally catch up and get the story about Anthony Carrillo Jr., 47, a 26-year veteran of the police force, when he was charged with tampering with evidence and abuse of his official capacity.

Laredo police officers arrested Ms. Villarreal in December 2017 and charged her with two counts of misuse of official information, a third-degree felony. They said the charges were in connection with her reporting on the 2017 suicide of a Customs and Border Protection supervisor, whose name Ms. Villarreal published.

For months before her arrest, the police department had also been hunting down the source of other leaks to Ms. Villarreal. They identified a police officer suspected of supplying the information — a woman who had worked on the force for 19 years — after searching the officer’s phone and finding hundreds of calls exchanged with Ms. Villarreal.

The department placed the officer on suspension for 20 days and said in a statement that the case against Ms. Villarreal involved an “obligation to the protection of a person’s right to privacy as it relates to sensitive information.”