Triss may not be there to cause trouble, but someone was still unhappy about Yennefer. That would be Olivia's sister, Cirilla.
Cirilla and Triss got along rather well. Triss was like a big sister that Cirilla never had. However, she did not really approve of Triss liking Geralt. She did not think that it was worth Triss' while.
Cirilla knew that Geralt truly loved Olivia and herself. He was way better than her biological father. Even so, she still remained proud and unyielding before him. She would never be like Olivia, who would take the extra step and act like a living doll to twist knots in the hearts of older men. Sometimes, Olivia would even mischievously go up to Geralt and mock his cringey acts in the process of picking up various sorceresses.
In Cirilla's opinion, a man should only love one woman. Look at how she and her sister had remained so loyal to each other. How could this good-for-nothing Geralt just casually plow all these sorceresses?