Presea's twin sister Sierra.

The only way to tell the two sister's apart is Sierra has a feather shaped bithmak on her chest

She makes her appearance throughout the anime's second season, corresponding with Presea's presence in the manga.

Sierra is pretending to be Presea to take away some pain of the Magic Knights, who blame themselves for not being able to help Presea, and of Ascot, who blames himself for killing Presea.

Clef falsely tells the Magic Knights that Princess Emeraude made a wish to revive all the people who died while she was imprisoned, but in fact, no one can revive a life once it is lost.

Sierra is in love with Clef, as was Presea.

She cannot make weapons out of Escudo, but she can help revive the weapons once they are lost.

(Source: AniDB)