I also read The Little White Horse when I was a kid! The style of Linnets and Valerians actually reminded me of it, so I checked and lo! it was the same author.

And I loved the description of Nan's hidden parlor. How lovely to have her own room with her own fireplace, all to herself!

It's too bad to hear that Gouge's adult books were so much more heavy-handed than her children's books, though.