My son and I are enjoying the Word Origins page-a-day calendar. They have it cheap at amazon. My son likes this kind of stuff too. She'd probably enjoy learning some simple/fun latin and greek - Rummy Roots is a card game for this, and English From the Roots Up is a nice book too.
Here's one kids' book
http://www.amazon.com/gp/product/081...lance&n=283155
But I've never read it.
Unfortunately this is a difficult topic to find in a children's book. It's probably a good thing for you to do as a read-aloud with her, so you can pick and choose the parts in adult books that suit you and her. There are GOBS of interesting books for adults on word origins.
Here's one kids' book
http://www.amazon.com/gp/product/081...lance&n=283155
But I've never read it.
Unfortunately this is a difficult topic to find in a children's book. It's probably a good thing for you to do as a read-aloud with her, so you can pick and choose the parts in adult books that suit you and her. There are GOBS of interesting books for adults on word origins.