Aery is an incredibly reliable source of damage in the early to mid game. It's also very strong in scrappy fights thanks to the bonus shielding on your [E].
WhyManaflow Band
Spamming abilities for lane pressure is Ori's forte and Manaflow Band enables her to do so very regularly.
WhyTranscendence
Stacking CDR on Orianna is a priority and in doing so you gain significantly more damage.
WhyScorch
The safe harassment range on your [Q] makes for an easy proc on Scorch for lane pressure damage.
WhyPerfect Timing
Zhonya's is a strong item on Orianna in many situations and Perfect Timing helps you hit that power spike even sooner.
WhyCosmic Insight
Cosmic Insight synergies very well with both Transcendence for CDR and Perfect Timing for a lower Zhonya's cooldown.