The Sword of Senack

In this middle grade fantasy, Aliya Fisher knows nothing about her true heritage until a vindictive sorceress kidnaps her brother and sister. The young adventurer must take up her birthright, battle eerie creatures, and find the Sword of Senack if she hopes to best the witch. But even if Aliya finds the famed weapon and survives the perilous oceanic journey, the enchantress is far more than she appears. How does one defeat an immortal who lusts for revenge?