If it's Lillie then I have a really crazy theory thanks to our chinese riddler which I'm sure won't be true. He once posted a picture of Anabel which means a girl who wears somewhat masculine clothes. Well, in XY we had AZ who was very loosely based on Odin. Lilllie might be very loosely based on Joan of Arc (connection to lilies and masculine clothes worn for some purpose). Or maybe there is no connection and she just changes midway when she gets serious because Cosmog got stolen or something.