it needs to be an indictable offense

She deliberately causes damage to goods as well as financial damages because the store has to clean up after her vandalizing. How is that not indictable?

Most states have codified the common law rule that a warrantless arrest may be made by a private person for a felony, misdemeanor or "breach of peace". "Breach of peace" covers a multitude of violations in which the Supreme Court has included a misdemeanor seatbelt violation punishable only by a fine. The term historically included theft, "nightwalking", prostitution and playing card and dice games.
(Wikipedia: Citizen's arrest).