Is the book Casey, Emma has the same surname – Clark – as Luna from Wild and Say No to Joe? Are they related?
This is just a case of a writer doing too many things at the same time and losing track of character names. I introduced Emma in the Buckhorn Brother books – Sawyer, Morgan, Gabe and Jordan – and totally forgot her last name.
Later I wrote Wild and introduced Luna Clark, then when I went back to write Casey, I realized Luna and Emma had the same last name. Please, ignore it and forgive me for sometimes being a ditz! (And actually, lots of real-life people have the same last name, yes?)