Naah, was she really just 12? Sounds unlikely to me, but well, what do I know.
Hi Bronnestam,
check out for the thesis of Franco Gurman "Teresa Carreno And Her Piano Music" on the web, it should be easily to find and download.

On page 67 of the thesis it says the following:
It is remarkable that at the age of twelve, Teresita was ready to show the world that she too could compose a ballade. Carreño’s Ballade in D flat Major, Op. 15 is of a
virtuosic nature. As far as its overall form, it follows this progression:
1) Introduction, cadenza, Theme A, Theme A slightly altered,
2) Theme B, Theme A altered more than before,
3) Theme C, developmental section,
4) Theme D,
5) Theme E, developmental section, Theme D slightly altered, Theme A
highly embellished, developmental section, restatement of Theme A
We shouldn't forget her EXTRAORDINARY development, she was pupil of her father, first, then of Gottschalk, who was her idol, and she was of an even younger age ( 8 or 9 ), when she composed, e.g., the Gottschalk Waltz, her opus 1.

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Hi 8av! I posted about this nifty piece a while back. I made the score available in this thread.
https://www.pianostreet.com/smf/index.php?topic=54166.0
cheers!
a.m. 
Hi ale, VERY MANY thanks to you!!

, and to bronnestam, too, but I too, had found the book easily available for buying, which I will, maybe, do additionally!
But, ale, that was super! Thanxx again and
greetings from: 8_oct!!