Authorities say Anna Ayala was taken into custody at her home. San Jose police spokesman Enrique Garcia says no details about the arrest will be released until a news conference that will be held Friday afternoon.
Las Vegas police also refused to comment.
Ayala told police she found the 1½-inch finger tip in her chili March 22 while eating at a Wendy's in San Jose. She said she intended to sue but relented, claiming the publicity was too emotionally taxing.
When police and health officials failed to find any missing digits among the workers involved in the restaurant's supply chain, suspicion fell on Ayala, whose story has become a late-night punch line.
Ayala has a litigious history. She has filed claims against several corporations, including a former employer and General Motors, though it is unclear from court records whether she received any money.
Ayala also said she got $30,000 from El Pollo Loco after her 13-year-old daughter got sick at one of the chain's Las Vegas-area restaurants. El Pollo Loco officials say she did not get a dime.
Wendy's International hired private investigators, set up a hot line for tips and offered a $100,000 reward for anyone who provides information leading to the finger's original owner.
Thursday, before Ayala was arrested, Wendy's announced it had ended its internal investigation, saying it could find no credible link between the finger and the restaurant chain.
The company says all employees at the San Jose store were found to have all their fingers, and no suppliers reported any hand or finger injuries.
Wendy's says that since the incident was reported, sales dropped off at franchises in Northern California, forcing layoffs and reduced hours in some locations.
By Josh Dubow