The first person who really changed Yennefer is Geralt.
Common ground that we can agree on...
Now if you want me to post some of what I consider "bad" sides of sides of Triss...
She should have been more confident in her abilities and should have tried to help Ciri by herself in BoE. After all, the fix was just magical in nature and both in the books and in the game the "rules" of magic are, well, almost non existent, they are never stated and usually what can or can't be done at a certain point in time is just a plot device to move the story in a desired direction.
Next, and even though I don't know the particular of that situation to the letter, she should have tried to teleport Geralt to Brokilon again at the end of the saga, instead of just watching him and Yen die.
She should have gone to KM immediately after Geralt asked to go and not spend her time sweet time somewhere until it was time for the battle against the WH.
I'm guessing she does something bad in b4, haven't read it read yet, finished b3 this afternoon and not sure to wait for the official translation or go for the fan translation.
Definitely not going to accuse of rape or similar shananigans, if anything she deserves a pat in the back for seizing her chance in W1.
Should have apologized to Yennefer for stealing his man though. (not sure if that happens off-screen or not).
Should have also apologized to her also for sleeping with him in the books. Even if they were broken up there are some codes between friends.
Should have stick around to help Geralt in Novigrad, even he doesn't say those three words.
And, got nothing else for now, I'll think of more...
Now your turn Yen folks, post Yen negatives