Build her as you would a neutral unit, but use the Atk+3 sacred seal (or Fury if you're not using Distant Counter and Water Breath, but instead Lightning Breath).
Give her Fury and Lightning breath(res refine), pretty basic build but it is effective
But if you want to use her water breath then, water breath(res refine) DC or CD then +atk seal
Pokemon GO
Fire Emblem Heroes
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