I was originally going to say she can do more for the State as Governor, but she's in her first four-year term, having taken the seat in January 2019, and can only run once more. That means she'll have 4 more years if re-elected in two years. Compare that with a Senatorial seat of 6 years, and no term limits, then it makes you think that maybe she'd be better off running for Senator.
The Senate is a tough nut to crack because of the six-year terms. Replacing the Deep Staters will take time, it’s much quicker and easier to focus on the House for 2022.
You inadvertently make a good case for why the legislature should still be picking the senators. An ambitious state legislator sees a “popular” governor might think ‘lets kick the Guv upstairs to be senator & that will pave the way for me to be governor”.
Why shoot for Senator -- go for POTUS, she has run a State, she is qualified.
A senator is a loser who makes deals all day with a bunch of other losers in the same legislative body.
There are two completely different personalities that gravitate to these positions.