There are 3 books in the WondLa series. The newest book is The Battle for WondLa which came out in 2014.

1
The Search for WondLa

Book cover of The Search for WondLa
Eva Nine was raised by the robot Muthr. But when a marauder destroys the underground sanctuary she called home, twelve-year-old Eva is forced to flee aboveground. Eva Nine is searching for anyone else like her. She knows that other humans exist because of a very special item she treasures ~…
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2
A Hero for WondLa

Book cover of A Hero for WondLa
Eva Nine has finally found what she has always been looking for; other human beings. Having been rescued by Hailey, Eva couldn't be happier, and now Hailey is taking Eva and her friends to the human colony New Attica, where humans of all shapes and sizes live in apparent peace…

3
The Battle for WondLa

Book cover of The Battle for WondLa
All hope for a peaceful coexistence between humankind and aliens seems lost in the third installment of the WondLa trilogy. Eva Nine has gone into hiding for fear of luring the wicked Loroc to her companions. However, news of the city Solas being captured by the human leader, Cadmus Pryde,…