The Shadow Girl by Ray Cummings

A mysterious tower appears in the middle of a city, bearing a troubled girl from the future in search of help from today. One of Cummings' best works, THE SHADOW GIRL remains thoroughly readable and enjoyable even though it was first published more than eighty years ago. "He is a Verne returned and a Wells going forward," remarked "Bob" Davis, dean of American magazine editors. "He is the American H.G. Wells," say other critics. Cummings has an unusual flair for things scientific as evidenced by the fact that while at Princeton University he accomplished the remarkable feat of absorbing three years of physics in that many months. His five years' association with Thomas Edison as the latter's personal assistant also added to Cummings's scientific knowledge. His bizarre early life, living on orange plantations in Puerto Rico, striking oil in Wyoming, gold seeking in British Columbia, timber cruising in the North, before he was twenty, also left its imprint.
"Leaving Mr. Edison's employ, Cummings began writing scientific fiction for many magazines. His stories gripped the popular imagination and they "clicked." Mr. Cummings's success as a writer has been meteoric, for in a few years he has become one of the world's most popular authors of scientific fiction.... --Argosy-Allstory Weekly, Feb. 8, 1930