She’s third in the chain right?
She’s second in the chain for PRESIDENT. She will not automatically move into the VP slot if Biden moves up. Obama and Biden would BOTH have to be removed for her to move into the PRESIDENCY.
If Biden moves up, he chooses a new VP and (s)he is confirmed by the Senate. Just like Agnew and Nixon and Ford. Gerald Ford was not the Speaker of the House when Agnew was booted.