I'm also midway on this. I don't think that Triss was being manipulative as far as the politics were concerned, but I do think she was atttempting to manipulate Geralt in the first two games for personal reasons.
In TW1, I think she made an understandable but badly-wrong decision to take advantage of Geralt's amnesia and let him think that she was the sorceress he was in love with. I don't think this makes her evil, or a bad person, it was just a bad decision made by someone who was in love and saw an opportunity to see that love go somewhere. We don't KNOW if she knew whether or not Yen was alive, but I think there's a decent probability that she knew and went ahead anyway. So yes, I think that there was manipulation involved, in that she didn't correct Geralt's assumption, she encouraged him to "remake" himself instead of trying to find out about his past. I think she kept her involvement with the Lodge secret not because she was plotting with them, but as part of this attempt to stop Geralt finding out about Yen.
In TW2, I think that she did mean to use the Rose of Remembrance to bind Geralt to her. Again, as the act of a desperate woman who would now have been panicking slightly as Geralt was recovering his memories, and had found out about Yen. Still a bad decision, but not evil (by my definition anyway). I still don't think she did anything sinister as far as politics were concerned - I think she was lied to by Letho while a captive, and simply made the mistake of believing him, and I think that the Nilfgaardians were lying when they said that Triss had revealed information to them. They were the manipulators in TW2, not Triss.
By the end of TW2, my head-canon is that Triss's conscience had kicked-in, and, if Geralt had romanced and trusted her in TW2, that she was the one who ended the relationship. (If Geralt had been played as suspicious of her by the end, then I think he probably ended it).
In TW3, she's exactly what she seems to be, there's no manipulation or machiavellian scheming going on.