Harold, who recently moved back downstate after living in Chicago for years, is embarking on a three-day campaign rollout in the central Illinois district.
She has never held office before, but had begun a primary campaign against former Rep. Tim Johnson (R-Ill.) before Johnson decided to retire in 2012. The Illinois Republican Party then chose Davis as his successor.
It's unclear how serious a threat Harold will be to the well-funded Davis, who's proven to be one of the strongest fundraisers of all vulnerable House incumbents. But he's already facing a potentially tough general election challenge from former Judge Ann Callis (D) in the swing district, and primary competition rarely helps a candidate.
Watch her campaign announcement video:
This post was first published at 9:29 a.m. and has since been updated.