Is she planning to run for Governor again?
More likely Senate. Feinstein is up in 2018 and the tides are turning against her. It would be a tough slog but doable. Oh and she'd have to run as a Democrat. I don't think a Republican could get elected in California in 2018.
The smart move would be to say she's switching parties because of Trump, run as a conservative Democrat left of Trump but right of the progressive wing.