Basically she is the better version of Keeva, the water esper.
This Build relies on high atkspd since her default attack lowers the cooldown of her purging shield by one second for each attack. On rapid with a atkspd shoulder she is able to stack her shield, if she can consistently attack.
There is no Champion who purges (enemy buff removal) better than espers. The tooltip for her Shield says "with each Zap" but the shield zaps twice for every second. So every second she removes two buffs off her target, for the whole fight, because her shield is never down. Furthermore the shield is a mulithitting spell, because each zap deals dmg and is therefore a great ultility to either raise dps on a tanky champion or get rid of enemy damage negotiation (coop) with fast mulitple hits.
Her ability to lower atk on default attack and lower def on her low cooldown second attack makes her the perfect buff advantage champion you can bring to your table. If you want no buffs on enemys but rather two of the most important debuffs on them, esper is the way to go.
She is useful absolutly everywhere, even in arena she brings a very disturbing fear to the table which can be clutch to mess up the enemy buff/kill rotation.
By ascending her she gains a total of 40% resistance what brings her in range of the desired 60% resistance with only one substat on one piece of gear. If you only 5* her yet, go with ATKSPD/HP/ACC, later on you should try to get ATKSPD/CRITD/HP with high HP and ATK subs. Also a CRITR of over 50% and ACC within the 60%. ACC is not as important for her since she attacks so fast and therefore often, even if you miss every second debuff application you wont notice much, yet her defbrake will not be relieable without 60% ACC. Same goes for her dmg, her shield zap and default attacks are so fast, if you reach about 50% CRITR you should be set decently. You do not have to build her overly tanky since she will always have a shild applied to her, therefore i recommend CRITD/ATK/CRITR stats. If you never get a leathal attack at what you are doing, there is no need for more tankyness rather than dmg.
Hope you guys enjoy my Guide
Best regards, Ninpo.