Was this one of the legendary heroes in the game's backstory?
She's one of the legendary heroes from Blazing/Binding Sword, the first 2 GBA games for Fire Emblem. She's suppose to be the wielder of both the sacred staff and the sacred light tome Aureola, having fought alongside Eliwood/Roy's ancestor Roland against the Dragons during the Scouring. She's also the founder of the religion in that world, the Saint Elimine Church, and is worshipped as a saint by most monks, clerics and troubadours.
Also from the look of it, she might actually be an ancestor to Pent and his kids, or at least Louise's side, as well. She looks really similar to Clarine and Louise, despite Louise not being born of royal blood. I'm actually surprised by that.