She is almost 11 now, but we are coding every day for almost a year now (I am logging the progress here: https://github.com/jackdoe/programming-for-kids). Its often we go to the number line :) but because we usually make games, and it was easy to get negative numbers when you go out of the screen, so it "clicked".
The whole game was her idea and we started working on it about 5 months ago.
You should mention that it was her idea and that you worked on it together on the web page! I'd buy it to support her efforts more than because I am sure my 11 year old would enjoy it!
One other thing I wasn't sure about it from the web page was how it was a game. I got the impression that it was basically just a set of python programs/ideas and you pick one at random. Is there anything game-like going on or is it just that?
The whole game was her idea and we started working on it about 5 months ago.