She's filled the serene, organized room with handsewn good and tied the look together with both natural elements and references to nature (a central theme of Montessori). As a Montessori educator herself she easily translates the tenets of the philosophy into the room's setup and the activities offered.
Meg's blog, Sew Liberated, is definitely one for your bookmarks. Start with her post on Finnian's room (with plenty more photos, a thoughtful description of the items in the room and why she selected them and links to many of the sources) and then have fun exploring! She also has an online shop for her sewing patterns.