Winter Spell (Chronicles of Mahon #1)

Trapped inside a crystalline sphere by a malevolent sorcerer, Mara spends her days planning her escape and nights using an enchanted mirror to observe her favorite warrior, Reika.
Reika, fierce leader of a band of mercenaries, has spent her life fighting for anyone who could afford her price. Betrayed by her clan, Reika is seized from death by the mysterious goddess, Mara.
Restless and unwilling to accept captivity, Reika vows to free Mara from the sorcerer's curse or die trying.