The magazine version used Reonn and the volume (latest) version used Leon. So I went with Leon because her name will eventually be shown in English in future chapters and I'd like to keep it standardised. Even though she will always be Reonn in my heart.
@Kinji
Thanks for the information about the names! If those are the names chosen by the official translation, I can't complain.
It's funny, since Leon is a masculine name and means "lion". So, a big cat. Perhaps she is secretly a trap or she has Western blood? Or both? That would be hilarious.