As with normal Sothis and her Sublime Surge; Snow's Grace neutralizes enemy "effective against dragon" bonuses, rendering her functionally immune to the bonus damage from weapons like the Falchion. In addition; it provides her with a flat +3 Speed, and the typical dragon adaptive damage vs. range.
The primary unique effect of Snow's Grace, however, is an in-combat boost of +5 to all stats as long as Sothis is at or above 50% health.
Neutralizes "effective against dragons" bonuses. Grants Spd+3. At start of combat, if unit's HP ≥ 50%, grants Atk/Spd/Def/Res+5 during combat. If foe's Range is 2, calculates damage using the lower of foe's Def or Res.