She's a control mage and she's very, very good at it.
The damage isn't strong early on, and her auto attack actually do a fair amount on their own for trading. She doesn't benefit from a Nashor's or Lichbane much unless the enemy team has little to no gap closers.. Though I still don't recommend them because she can self peel herself insanely well.
She's free form kiting machine and she does a hell of a good job of keeping control of the enemies positions with her ball. You can punish opponents heavily for ignoring it's position.
Things to remember as her:
The Q damage gets better with items and is better for denying CS early on than straight up harass as you want to use it to punish someone for going in to farm. It's intentionally a small range to cast because otherwise it would be way too powerful. The range of her ball before it returns is actually fairly big, so it allows you to place it in a spot and stay a pretty safe distance away to cast it towards your direction. CDR is really good for her cause it allows her to constantly position her ball.
The W can be cast right after the ball has landed at your targeted when you Q and adds into trading. The slow and speed boost you get from it allow you to self peel and generally keeps you at a safe distance from melee champions even when they have a gap closer.
The E gives both resistances to yourself when you're holding it and allows you to cast it on yourself for a shield. If you give the ball to an ally it also gives them the passive resistances as well (keep that in mind for your engage champs so they can have a bit of resistance when rushing in. It's also noting that if you self cast the E or on an ally, if the ball collides with an enemy on it's travel it will damage them. This is good for wave clearing, since you can Q forward into a minion wave, W and then to to yourself (making sure to hit as many targets with it's collision).
She excels well in engage and disengage comps and can be good for anti-sieging and peeling for her teammates. She's actually fairly balanced and fits most, if not all, comps because of her ultimate.
Azir on the other hand, while good at being a control mage as well, has to be more strategic with his soldier placement. Orianna has to be good with her ball placement as well but she's able to cast her ultimate from a much safer distance while Azir has to get into the enemy team to make good use of it.
They both have their strengths and weaknesses, but I personally think Orianna does a slightly better job.
