I think a cut scene with Yen and Emhyr would be in order, as an exposition of their relationship. Honestly, we've had two games showing us what Geralt and Triss were doing, but there is only a vague explanation about what Yen was doing that entire time.
Remember, she was returned to the native world long before Geralt, basically since Geralt traded himself for her.
So, she was with Letho shortly before falling in Emhyr's hands, so much time to talk about with Geralt, I would've thought. It just seems silly she was waiting for Geralt to restore his memory that whole time, while futilely doing magic tricks to find Ciri.
Either a long convo with Geralt or some cutscene to better explain her time alone. A much longer time than both Witcher 1 or 2.