Then Jill will have Brandon nominate HER for VP
25th amendment.
Jill becomes president.
“...
Amendment 25 Section 2.
Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.
.....”
So still has to be approved by Congress. I doubt if Jill would get the approval.
President and veep cannot be from the same state.