A normal alternate history would have points of to explain why this world features a vaguely post-WWI situation, with a League Nations that the American Republic belongs to, albeit with an Incaztecan Empire, and the Celestial Republic, among others. This one has a work -- read by the title heroine -- explaining how alternate universes can converge, and this one started out much different. From the ancient civilizations evolved from the maiasaurs to its many successors, leading to the American Republic founded in year 17 -- what happened in 1774 was an attempt by King George the Mad to subjugate them. (They once had an ambassador from the United States of America appear out of nowhere and vanish too, after discombobulating everyone with his inability to see superheroes -- excuse me, personas -- using their powers -- excuse me, gifts -- in front of him and remembering a trip to the Moon by chemical rocket.)
Into this converging world, the title character throws some chaos. She (at the age of twelve) attempted the Maze containing the marvel of the Namestone, which, everyone knows, can bring about Utopia, and succeeded. She is, in the opening, confronted with League forces demanding it, and refuses.
Fortunately for her, though her efforts were broadcast world-wide by the Maze, the broadcasts obscured her appearance and language. She goes off to recuperate, the Legion of Nations has much posturing about her duty to hand over the Namestone and the necessity of execution for her disobedience, and the nations that will regard any attempt to send forces to catch in her their territory as an act of war. The Lords of Eternity make their plans, which do not give humanity much consideration. Three minors, a girl and her younger twin brother and sister, live in Massachusetts and have complications with their powers.
It includes buying books, an invasion of the American Republic, Incaztecans trying to pretend to be Prussian, the Divine Wind, the Wizard of Mars sending letters, creatures who live in the sun, a character from another world, and more.
It's the first book of a trilogy, and there are many threads that are started but not finished here.