It really helped her learn the planets better and we even did one of the projects out of it teach just how far apart things are on a visible scale.
It is -- http://www.amazon.com/Planets-System-Lets-Read-Find-Out-Science/dp/006445178X
The planets in our solar system by Branley
There are tons of kid solar system books out there and I just encourage you to start young with kids and science! Never too early to teach the scientific thought process and help them learn more about the world around them.