The VP's confirmation would be beneficial, solidifying their position for re-election. However, if the confirmation fails, it could reflect negatively on those responsible, particularly if the candidate wins the general election, as it would highlight their inability to secure a key appointment. Regardless, the process would attract extensive media attention, offering free publicity, which is a win.

The problem is that the Republican controlled house would have to confirm the appointed VP. The senate might take a minute, but it would likely get it done.

Yeah, I meant the house: it would be much in the majority's interest* to leave the position vacant through the election.

* I mean the way they seem to operate these days, where keeping the system running properly isn't considered important, and to a hardcore group is considered something to firmly oppose.

Note that by the 25th Amendment both houses would have to confirm. The (bare) Democratic majority Senate would be a challenge. The GOP majority House an even stronger hurdle. Though confirmation is a simple majority, not a supermajority (2/3 vote):

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.

<https://www.law.cornell.edu/constitution/amendmentxxv>

There's also the fact that in ascending to the Presidency, Harris would no longer be President of the Senate, which would lose her tie-breaking vote, AFAIU.