Short answer: They have a somewhat shaky case, but there is very little chance of this happening.

Long answer: The evidence that Ethel Rosenberg was a spy was always thin compared to that against Julius Rosenberg. The Venona and KGB files have definitively established that Julius Rosenberg was an active and dedicated leader of a spy ring that fed information to the Soviet Union. He was recruited by the KGB in 1942 and supplied them with thousands of documents about airplanes and a complete proximity fuse. Julius Rosenberg also helped recruit his brother-in-law David Greenglass who was working on the Manhattan Project, and he passed along information on the atomic bomb.

However, Ethel's involvement in espionage is more questionable. By all accounts, Julius and Ethel were deeply in love and devoted to each other, so she almost certainly knew about his being a spy. There is a Venona cable that refers to Ethel as "sufficiently well developed politically" and says that she knows about her husband's espionage and that of a couple of other members of the spy ring.

When the police arrested David Greenglass and Julius Rosenberg, they were trying to find additional members of the spy ring. David Greenglass agreed to confess and become a witness for the prosecution in exchange for a lighter sentence, but Julius denied any involvement in espionage. To put further pressure on him, the police arrested his wife Ethel and charged with espionage, in the hopes of getting him to give up more information.

Moreover, during the trial David Greenglass claimed that his sister Ethel helped Julius recruit him and his wife Ruth Greenglass to engage in espionage, and that Ethel typed some handwritten notes explaining the diagram of an atomic bomb. However, many years after the trial David told a journalist that he lied about Ethel's involvement in order to protect his wife from prosecution. These newly released grand jury transcripts, in which David makes no mention of Ethel's involvement, provide further evidence that he probably didn't tell the truth about Ethel.

To answer some questions: Was Ethel Rosenberg innocent of espionage? No; there is good evidence that she knew about and supported Julius's spying for the Soviet Union, and probably assisted him in some ways. But we aren't sure how much she helped him.

Did David Greenglass exaggerate her participation in espionage to protect his wife Ruth? Almost certainly, yes. And his testimony was a central part of the legal case against Ethel. Without that, it is possible that the jury could have found her not guilty.

So, Ethel was a spy (although we're not sure how important, and not as important as the prosecution claimed at the trial). However, the legal case against her was weak, and probably wouldn't stand up in a modern-day court. So there is truth to the claim that she was unfairly convicted.

As for Ethel's being exonerated, I think it is very unlikely that will ever happen. The U.S. government usually exonerates people only when there is clear evidence of innocence, and here that's not the case.

Sources: "The Rosenberg File" by Ronald Radosh and Joyce Milton. Amazon link here: http://www.amazon.com/The-Rosenberg-File-Second-Edition/dp/0300072058

"The Brother: The Untold Story of the Rosenberg Case" by Sam Roberts.

http://law2.umkc.edu/faculty/projects/ftrials/rosenb/ROSENB.HTM