I don't know who Robin McKinley is (although I have just googled her and saw she is an author).

We chose Aerin because we loved the name Erin, but there is a tradition of "A" names in my partners family, so we added the A to the front, but it's pronounced the same as Erin. It's a spelling I hadn't ever seen anywhere at that time, so we didn't get it from anywhere. It's a name that has personal meaning for us.