Waves of nostalgia! I remember loving Tottie Plantagenet (not least for her extraordinary name), and am so glad you reminded me of The Doll's House. The subject of dolls made me think of a book I remember from second grade -- I don't think it was one I ever owned, but I retained some vivid images of Japanese dolls and the name Plum.
A bit of online searching, and it turns out to be another book by Rumer Godden, the unfortunately now out of print Little Plum. It's apparently the sequel to Miss Happiness and Miss Flower, which tells the story of eight-year-old Nona Fell (like Sara Crewe, a recent transplant from India to England), trying to fit into the family of her aunt, uncle, and cousins, and to handle her loneliness and outsider status. Nona (proper) and her cousin Belinda (tomboyish) receive two Japanese dolls, Miss Happiness and Miss Flower. Over the course of the book (and due partly to the machinations of the two dolls, who can speak to each other, though not to the girls), they become friends, and build and furnish an appropriate Japanese-style dollhouse for them. A third doll, Baby Peach, joins them. While I don't remember reading this book at all, online reviews wax poetic about the glories of the actual plans for dollhouse and furniture that Godden included in the book. Evidently, you can really build it from these plans.Little Plum, the sequel, involves a rich family moving next door to the Fells' house. The rich girl has a Japanese doll as well (that would be Little Plum), but doesn't take good care of her. It's another story of girl friendship growing despite initial animosity, and the dolls have their own friendship and communication beneath the girls' notice. That's part of what I remember about the books, that and a climactic scene involving a doll falling out of a tree.
For a slightly younger age group, there is Beatrix Potter's wonderful The Tale of Two Bad Mice. Two gloriously named bad mice, Tom Thumb and his wife Hunca Munca, break into the dollhouse populated by two sentient but immobile dolls, and destroy lots of things in their search for food and items to steal. The fake food on the dolls' table is infuriating. It is terribly funny, and has a nice little moral at the end, as well as some great illustrations of how Hunca Munca uses some of her stolen booty when she has mouse babies in her hole. 
I know it's not quite the same thing, but this thread made me think today for the first time in years about the series The Littles, by John Peterson. It's a big series, with lots of sequels, and I remember gobbling them like candy in elementary school, where they came super-cheap as part of a Scholastic catalog. I think I knew at the time that they weren't great books, but oh, they were fun. The Littles are a family of tiny almost-people (they have mouse-like tails) who live in the walls of the house of the Biggs. They get into all kinds of adventures, and danger lurks around every corner. There's something so appealing about the idea of tiny communication, be it doll or person.In answer to your question about Mona Baby, I'm not sure how Eleanor feels about Isabel co-opting her. I know that Eleanor still does consider Mona Baby her baby, but she's been very generous about letting Isabel play with her. We shall see.
I collected final portfolios this week, and so have asked a few friends to help me out again, as several did this winter, by providing guest blogs for a couple of weeks while I am up to my neck in student writing. Look for Ian's mom Holly's take on books with maps in them on Monday.
Love, Annie
