Katherine blood may not be the cure but may be an ingredient to make the cure. Esther has used Tatia and Elana's blood for powerful spells including the vampire imortatality spell. So maybe it need to create another cure.
Anything is possible but also I think that a witch is needed to do it as well. Since Bonnie will be a ghost, they either need to bring Bonnie back so she can make the spell or maybe Qetsiyah and Bonnie will be both resurrected and can make it together.