Triss is really good character, she is young (and that is important) and quite a lot affected by her relation-ship (short love affair) with Geralt and by wounds that she suffered during battle of Sodden.
Her first appearance is there when Geralt asks her for favour and she help him with Ciri. She is presented as quite good friend of Morhen witchers and she still loves Geralt. He considers their love affair as HIS mistake. She is presented as very kind and good character in that chapter. She tried to seduce him, but when he resisted, she simply give that up (for readers - during 2nd case she was very sick
), even when she loved him so much. He told her, she is his very good friend and she always will be.
After that she goes through big decission. She bacame member of the Lodge, which is the best side for her, but after that Yennefer 'betrayed' Lodge and worked alone - some people blame her for being there ("hiding in Lodge") but there is not even mentioned that Yennefer gave her chance to cooperate with her. And she was quite young for the way of acting, which Yennefer chosed.
She regreted a lot that she couldn't help more to Ciri or Yennefer or at least fight during second war with Nilfgaard. There is clearly visible, what good charactrer she is. But as she said, other members of the Lodge explained her well, what is important to do and what is their role. They simply convicted her with rational arguments. So if you want to blame her, you can just blame her for being not so much emotional and strong as Yennefer.
She is very good friend of Ciri. She dressed witchers down for their mistakes about Ciri and she protected her there. She is like her older sister.
In the end she believed, Ciri would be safe in Lodge. Little bit later she is still arguing with Yen about Geralt (Yen never forget what was between them), but one moment after that Triss saved her life during that pogrom in Rivia. That is important moment, because there is expressly mentioned how she could chose between that hiding in the Lodge and helping to her friends and what she decided to do.
My conclusion - Triss is the best friend of Geralt. I would never blame her for being in Lodge, which was the best side (not only for her). And I cannot also blame her for not giving herself up to Vilgeforz just like Yen did.
In the most important moments, when she COULD decide what to do, she chosed the right things (she helped Geralt, when he needed, she helped Yen, she voted for Ciri, in game she saved Geralt's life - I almost forgot, she did that also after Thanedd dispute - and even when she had nice moments with Geralt - during W2 - she offered him help to search for Yennefer).