You left out Mendocino and particularly Anderson Valley. A stop at Navarro will get you all most all the whites you need.
Good call -I believe the tasting is expensive but they make a class product. I am looking at their winery from my bedroom as I type! Jennifer Lamb has a Sauvignon Blanc that many people like - downtown St. Helena (Herb Lamb Vineyards/Two Old Dogs).
Peter Michael Winery just outside Calistoga in Knight’s Valley might be something to look at.
“She’s a primarily semi-sweet white wine drinker”
Take her to Sattui. Yes, I’m serious.
A little south of where you were looking for recommendations but she might like Vine Cliff.
Nothing fancy but seems to fit your ask. Check out Laird, O’Brian and Materra. Good selections of Whites and Reds. Nothing spectacular but they don’t suck. All south of Yountville.
another vote for massican…wine’s are great and Dan is a good guy to taste with
It’s been a blend and a 100% chard. It started as a blend, and it’s back to being a blend now.
My wife likes the whites at Cakebread and St. Supery in addition to a bunch of the already mentioned.