Asking for my girlfriend. She lives in WA where we do not have a car there but visits me in CA frequently. And we have our car in CA, which she needs to drive. She does not have a WA license and does not plan to have one for WA. Since she does not need one.
You have to reside in California to hold a California driver's licence
Since your girlfriend lives in Washington she can't get a California licence. The good news is she can get a Washington licence and use it in California.
More generally, most places in the world allow "foreigners" (interstate OR international) to use their foreign licence to drive.