I agree with you completely, you can say she was a Sith all along and that she was just kidding herself. But ultimately, much like the Son said on mortis, Sith is a title, but it is not who she is. She uses the dark side, yes - but she does not follow the Sith code. The Force certainly does not free her.
Great post by the way Aurbere, very interesting to see your interpretation of the Malachor business. I always thought it was a ruse to bring Meetra there to confront her past. But perhaps it was a mixture. Thoughts on Arren Kae anyone?
She had taken up the title of Darth Traya, but that might have been, more than anything, her choice to do so and not reflective how she really felt. We all know that she was Dark Side. At least, what she planned to do would be Dark Side. I think she had fallen to the Dark Side, but didn't consider herself Sith. She considered herself above the Sith, in a way, for she was using them to accomplish her ultimate goal.
As to the Malachor business. It was a mixture, I think. Malachor was the, probably, the worst moment of Meetra's life. No doubt Kreia wanted her to face Malachor one last time. But above all else, she wanted to tell Meetra the truth before enacting her plan.
Arren Kae? I don't know. Kae was a Jedi that fought in the Mandalorian Wars with Revan. Her and Kreia have similarities in their backstory. The similarities are definitely there, but, if we are referring to them being the same person, I can't comment or speculate. There is one glaring flaw in this comparison: Kae fought in the War, but Kreia did not (so she says
). For now though, we can say that they were both Jedi Historians and were both exiled for teaching Revan.