In a statement, police say she admitted to poisoning her husband "without his knowledge".
She was arrested and held in custody on Friday. Police have not announced any potential motive.
Mr Clayton, who founded a physical therapy company, was pronounced dead after appearing to suffer a fall down stairs in the foyer of his home in the upmarket neighbourhood of Clover - about 20 miles from Charlotte, North Carolina.
A funeral was held for him in the couple's backyard in early August - friends and neighbors say - before investigators discovered his cause of death. Complete story here