Thoughts and description on the Elizabeth Goudge website.
Henrietta's House is pure Elizabeth Goudge, all the way through. There's just no way you could mistake it for anything else. It belongs squarely in her low fantasy-anything-could-happen realm along with The Little White Horse, seems to be written for about the same age group, and in fact it was published the year before LWH. I wonder if she was working on both books at once, or if LWH grew out of the ideas in Henrietta. (There is some information on the writing of the book at the link above.)
In any case, Henrietta's House is a fairly short novel (about 150 pages), set at the end of horse-and-carriage days. Henrietta is a sensitive young girl living with old, strict relatives because her poet father is almost never around. Like Susan in Miracle on 34th Street, she wants a house; not because she has nowhere to live, but because she dreams of a true "home," where (she assumes) her father will also stay put.
She's not the only one around with dreams and wishes. Unusually, for a book that seems to be aimed at children, most of the other characters are adults, and some of them are quite old--too old, children might think, to be making wishes. But this is the day that everybody's wishes, improbably enough, come true. It's her adopted brother's birthday, and he invites a somewhat motley crew of oldsters to a picnic in Foxglove Combe, along with a young aunt and uncle who shock everyone with their new motorcar. But the vehicles (including the car) all take wrong turns and get separated on the way to the picnic, and by the time they're reunited at the end, each person has had some kind of adventure and/or awakening.
They meet up, one by one, with a large, cross old man who has a bad habit of sticking pins in wax figures (foreshadowing a similar theme in Linnets and Valerians?), but who also seems to be drawn from The Selfish Giant. Who is he, and does he fit in somehow with the old local legends of robbers and hermits? And who was that other old man who came into the bookshop and bought up the entire list of Henrietta's favourite books? (If you want to see the list, you'll have to read the book. There were a few I'd never heard of.)
Considering the themes that Goudge explores in her WWII/postwar novels, such as hunger (physical, emotional, spiritual) and feelings of displacement aggravated by war and shortages, books like LWH and this one seem like her version of comfort food. The motorcar, for instance, somehow disappears at the end of the story: everyone agreed it didn't belong. There are shops with all the books you want, kitchens with all the nicest kinds of food, and characters who...even the bad ones...can reform if they can just remember where they left their hearts.
Henrietta's House is the third in a trilogy, but it can also stand just fine on its own. (But now I want to go back and read the first two.)