Ms. Shanahan, 38, a onetime Silicon Valley lawyer, has never held public office and has scant name recognition. But she was selected after Mr. Rodgers and Mr. Ventura fell through as vice-presidential candidates and Mr. Kennedy’s campaign needed money to fund its efforts to get onto state ballots, three people familiar with the events said. And money was something that Ms. Shanahan could provide in abundance.

Ms. Shanahan has a fortune of more than $1 billion that stems largely from her divorce settlement last year with Sergey Brin, a founder of Google, whose net worth exceeds $145 billion, three people with knowledge of her finances said. During their five-year marriage, Ms. Shanahan partied with Silicon Valley’s elite and used recreational drugs including cocaine, ketamine and psychedelic mushrooms, according to eight people and documents reviewed by The New York Times. Ms. Shanahan and Mr. Brin separated after she had a sexual encounter with Elon Musk in 2021, three of the people said.