Foster, 64, of Willingboro, is a veteran of the Air Force and president of her township's chapter of the NAACP.
After serving nearly two decades as director of Willingboro's senior center, she is the executive director of the township's Community Affairs Department on Aging and Veteran Affairs.
Foster could not be reached for comment but said in a statement that she looked forward to bringing her experiences "to the campaign trail to continue fighting for the taxpayers."
Donnelly, a former Cinnaminson mayor, has been on the board five years.
Foster's running mates are James Kostoplis of Bordentown, who will challenge Sheriff Jean Stanford, a lawyer from Westampton who has been in office 12 years, and Nancy Youngkin of Medford, who will oppose County Clerk Tim Tyler of Fieldsboro, who was elected in 2008.
Kostoplis, 59, a retired Hamilton Township police lieutenant who later worked as a chief warrant officer for the Mercer County sheriff, said he had "a whole lot of experience when it comes to the functions and responsibilities of the Sheriff's Office."
Kostoplis is also a fire commissioner for Bordentown Fire District No. 2 and a part-time private security officer.
Youngkin, 48, a hair stylist who ran unsuccessfully for Medford Township Council last year, said she had also worked in public relations and marketing, "professions that strongly rely on meeting people's needs and building relationships."
She also has been a parent volunteer in the town's elementary and middle schools.
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