Regardless of current standing, Asajj was once and should now be, Sith!

My opinion is there aren't enough Sith for any sort of synergy. Get more Sith or just remove the tag and switch to "Dark Side" or something.

If she was considered even an ally at one point I think its would be acceptable to add Sith label for gameplay/balance reasons.

You can be as technically right and true to the source but they never wrote the books movies to make sure a mobile collecting turn based squad battle game is balanced.