I'm not skeptical that she voted illegally, but I'm skeptical about the five times in just a 3 year period. Is this "five times between 2012 and 2014" aspect of the story true?
No. That's apparently newspeople playing the game of telephone (Fox isn't the only organization that got it wrong). She did vote five times, but that occurred between 2004 and 2014. From a report on her arrest in November 2015 by NBC-DFW.com:
Dallas County Elections Administrator Toni Pippins-Poole said records showed that Ortega had voted a total of five times. The first was in the Republican primary in 2004 and the most recent was the Republican primary runoff in May 2014, Pippins-Poole said.
She was found guilty for two of those acts on Wednesday, February 8, as reported by the Dallas Star-Telegram:
A Tarrant County jury found a Grand Prairie woman guilty Wednesday of two counts of illegal voting and is set to resume deliberations in the punishment phase of her trial Thursday morning.
Rosa Maria Ortega, 37, was found guilty of voting in the November 2012 general election and the May 2014 Republican primary runoff in Dallas County “when she knew she was not a United States citizen.”