She is studying to become a social worker in Jaén, in southern Spain, and declined to be interviewed, saying the case had brought her and her family enough trouble. But in an email exchange, she said that the intention of her Twitter posts was to fight “a system in which a minority lives on the back of the death, misery and exploitation of a majority,” in a country where the euro crisis has sown widespread economic despair.

Image Alba González Camacho, 21, posted messages calling for politicians to be killed.

“The truth is that I’m a very normal girl, who has never landed herself in any kind of problem,” Ms. González Camacho said by email. “But if I tell you everything that I’m fed up with, I would never stop.”

“I never imagined something like that could happen to me because you find a lot of nonsense on the Internet, including worse than mine,” she wrote about her conviction. “But it seems that here that the prosecution is only for those from one side — the Fascists can say whatever they want, and nothing will ever happen to them.”

Her lawyer, Miguel Angel Gómez García, suggested the case showed the “thin barrier” between freedom of expression and antiterrorism rules, and that Ms. González Camacho had been made a scapegoat. .”

The case comes as the conservative Rajoy government is eyeing other restrictions on public protests, including the political use of the Internet, having agreed in November to a controversial draft bill that would make it a criminal offense to use the Internet to organize any violent protest action. Esther Giménez-Salinas, a professor on the criminal law faculty of Esade, a Spanish university, said that there had been few legal cases against apologies for Nazism by far-right groups. In terms of freedom of expression, she said, there is a problem “if only specific opinions are forbidden.”

Most of the terrorism Spain has experienced has in fact come from separatist or far-left groups, though the country suffered a litany of human rights abuses under the Fascist Franco dictatorship that ended in 1975. A group of Islamists were convicted in connection with the country’s worst bombing attack, which killed 191 people in 2004 at the Atocha train station in Madrid.

The last victim of the far-left Grapo, whose full name is the First of October Anti-Fascist Resistance Groups, was a businesswoman, killed in 2006 during a botched kidnapping attempt. The group’s historical leader died in 2001, and three years later 24 Grapo members were convicted in a high-profile case led by Judge Baltasar Garzón.