I haven't read all the replies, so maybe this has been mentioned and dismissed, but have you read Ramona books to your daughter? I am not sure that I would call them poetic, but they are certainly full of real emotion. My daughter, who is almost five, has loved them for several years.
I'd also recommend the Betsy books by Carolyn Haywood. Again, they are not poetic, but they are lovely and sweet.
How about My Father's Dragon (and the succeeding two books)? How about Rabbit Hill? The Moffats (Eleanor Estes)? All-of-a-Kind Family (Sydney Taylor)? The Five Little Peppers series? Miss Hickory? OH! I know! How about the Catwings series by Ursula K. LeGuin? Pippi Longstocking? The Wind in the Willows? Just-So Stories? The Jungle Book? The Secret Garden? Caddie Woodlawn? Plain Girl by Virginia Sorensen (one of my childhood favorites, about an Amish girl whose brother decides to leave the Amish)? Trina by Patricia Miles Martin (another childhood favorite)? My dad used to read me a fantastic book called Indian Tales for Little Folks (does anyone else remember the Terrible Old Ulagoo?). We just watched the movie Ella Enchanted. We haven't read the book, but the movie was fantastic. What about some of the colored fairy books, like The Blue Fairy Book or The Yellow Fairy Book? Maybe you could check out Ambleside's reading list. They have a lot of older books on their lists.
ETA: Your daughter might really enjoy Sarah, Plain and Tall and its sequels, Skylark and Caleb's Story. Anna and Caleb's mother had died before the story starts, and it is mentioned that she died in childbirth, but it doesn't happen in the story itself.
Also, I heartily second some suggestions I saw that I hadn't thought of: Mr. Popper's Penguins, A Cricket in Times Square, Mrs. Frisby and the Rats of NIMH, and Trumpet of the Swan, and Old Mother West Wind stories by Thorton Burgess. My dd thoroughly enjoyed all of these books.
Additonally, I understand your hesitation with the Magic Treehouse books. They are by no means great literature. However, my kids have learned vast amounts of history from them and the books have been a steppingstone to further and more in-depth study of many of the topics we first encountered with Jack and Annie: rainforests, Egypt, Greek myths, India, etc.
Namaste!