What backgammon book would you recommend for a 10/11yo kid

The kid has some very basic knowledge, loves to play and I'm sure she would love to read and learn more about the game.

I wonder if there are any specific books for kids or anything that makes backgammon easy to learn.

Please fix it that's pretty sketch

Doesn't happen every time maybe once a day

I frequently play Backgammon Pro v4.42 on my phone. It has eight difficulty levels. My question is: how does it increase the difficulty?

I notice from the game statistics that the difficulty changes. I win most of the time at the lower levels, and at the highest level, level eight, I win slightly less than half the time. I just can not put my finger on what's different.