Core: Philo, Chalice, Aegis, Merc's Treads/Ninja Tabi
She's squishy and needs to be built a little tanky. Tear is garbage, Chalice is godmode, with Grail basically her Infinity Edge.
Aegis is godly on her if you max out her W early. Almost gives everyone free Chain Vests and Negatron Cloaks, plus more on whoever you're healing. Rank 5 W and Aegis in a mid game team fight is backbreaking.
Shurelia's + Grail + masteries will nearly reach CDR cap.
She doesn't need a ton of extra health, Aegis and Shurelia's should be okay, armor and MR make her self-heal more efficient.
MP/5 from Philo and masteries, multiplied by Chalice/Grail, gives her infinite mana, I think I've hit over 120 MP5 with certain builds.