She was attorney general of California a long time ago, so there's no doubt in my mind she could win the governor position.
Her presidential run will have no effect on her odds of winning governor since she'd only have to appeal to Cali voters who she won during the November election. Ain't no Republican winning California, just like there's no Republican in NYS that'd win New York.
I think she'd be considered preferable compared to Newsom, whose approval rating has declined every year; what's crazy is that people outside of California think higher of Gavin than his own state residents. The only reason why Newsom had Cali under his grasp is that he didn't have a worthy opponent; Kamala would definitely give him a run for his money in a primary if he were to decide to continue as Cali governor since he can't run for President, and governor at the same time.
If Newsom declares he's running for the presidency in 2028 then Kamala would be a lock to win the gubernatorial seat. The only way she'd lose is if a better Cali Democrat arises, but the thing is that California doesn't really have strong Democrat politicians, which is one of the reasons why Newsom won his elections easily because the competition was sparse.
Hypothetically, Gavin's gonna have to decide whether to stand pat as gov or risk losing his governor seat for a chance at the presidency, which he may win or lose, and let's say he'd lose that would mean he'd be out of politics altogether in 2028 if he were to fail that year's November presidential election.