Probably because she's ambiguous enough that the devs decided they could get away with denying her any faction synergies. She was Darth Nihilus' apprentice originally, so she started as a Sith, but she betrays him to join the Jedi Exile practically as soon as she's introduced in KotOR2. And since the Jedi Exile is, well, an exile, you could well argue that joining her does not make the no-longer-Sith Visas a Jedi, since she isn't technically affiliated with the Jedi Order. (Sort of like Ahsoka, except that in Ahsoka's case it was voluntary.)