Why not just use Arlo? It would fit right in with Marlowe and Harlow nowadays.
I have a bad mental image of Roxanne/Roxy, I've just known so many...not so ladylike, shall we say...girls named Roxanne. It's kind of a "trashy" name in my neck of the woods. Olivia is nice, but I agree it's way to popular. What about just Liv? That's pretty spunky.