It's an interesting point in the clone wars TV show. After she is betrayed by dooku, she goes to darthotmir, from where she was taken as a child. Mother Talzin meets her and she promises her revenge. Before doing so, she undergoes a baptism style ritual to join the Nightsisters clan. As part of which, she renounces all other alleigiences, particularly (highlighted by Talzin) to the sith and her former master.
As such, amusingly, if they gave Asajj the Sith tag, they would actually have to remove the Nightsister tag, as she was never both at once. And nobody wants that.
Also worth noting, towards the end of the clone wars TV show, she eventually becomes a bounty hunter, and one of her first jobs is on heist with a team including boba fett, dengar, and bossk. I don't see anyone asking for her to be a Bounty Hunter though.