To the people commenting on/reporting this: the question is fine; our current events rule permits discussion of events through 1996, inclusive. We approve or remove every question that gets asked here and this one is approved.

Thanks!

The National First Ladies' Library has an article on this from 2013, they cite Elanor Roosevelt as the first spouse to speak at a nominating convention at the 1940 Democratic convention. Pat Nixon was the 2nd to do so, in '72, followed by Nancy Reagan in '84, Barbara Bush in '92 and Hillary in '96. The first non-First Lady to speak was Elizabeth Dole, also in '96.

http://www.firstladies.org/blog/candidates-spouses-who-spoke-at-national-conventions/

Barbara Bush gave a speech at the 1992 Republican National Convention. Her husband George H.W. Bush was both a candidate and the incumbent President at the time, so I'm not quite sure if this fits the mold of your question...but technically Bush Sr. was a candidate in 1992, and his spouse Barbara did give a speech at the RNC, although she was obviously the First Lady at the time. Here is the transcript:

http://www.speeches-usa.com/Transcripts/039_bush.html