This article contains spoilers!
Formerly, she was supposed to be one of the bosses in the Sisters of Moon encounter, but Blizzard either changed their mind (as she got replaced by Huntress Kasparian) or she was put up in the journal by mistake.
Naisha is haunting the Tomb as objective of the Tomb of Sargeras: Lost But Not Forgotten world quest. Such an iconic character and opportunity wasted. She could have been involved to help players understand reasons for Maiev's hatred toward Illidan, especially because they both (her and Illidan) are assisting players inside the Tomb and character interaction would be more than appreciated.