Rida Ali, one of Monte McNaughton's staffers, was arrested last week after Tory MPP Christine Elliott's campaign said they received a series of threatening text messages.
She appeared in a Toronto court on Monday and is free on bail.
Details of the alleged threats are subject to a publication ban.
Neither the McNaughton nor Elliott campaigns commented on the matter.
Elliott, McNaughton and federal Conservative MP Patrick Brown are vying to replace Tim Hudak, who resigned last year.