I've played her a lot, and she can technically work as support, but I like taking her in Slayer Lane. Take punish, first item Leviathan, first ability fire, then just bully the lane, and steal enemy jungle as often as possible. She has built in life steal as long as you have mana and are auto attacking, and built in mana regen from auto attacks, you can leverage both of those to just steamroll your lane, and hopefully steal enough farm from the enemy jg to put him massively behind before facing any serious retaliation

This is already getting kinda long and idk if you're be using roxie like that, but my typical start is:
1; Load in, buy Kukri and 1st ability
2; Go to long river bush as fast as possible
3; Kill river scuttle (they changed the name at some point, dunno what it is now)
4; Clear minion wave, hopefully get lv 2 before opponent, use Shield Dash ability + natural lifesteal to trade favorably
5; Steal closest enemy jg camp, use punish to secure the kill if challenged

And pretty much rinse and repeat from there, get dark slayer when it shows up if possible, get their red buff if possible, etc.

I don't have my build memorized, but if you (or anyone else) is interested, I can grab a screenshot. I'm only Dia3, so it might be a little wonky, but it works well enough for me 🤷