I don't know if this is a bug or not but after finishing the game, you can actually find Keira at Kaer Morhen. You can only have this scene if Geralt convinces Keira to go to Kaer Morhen during the quest "For the Advancement of Learning".
Apparently there is a followup scene if you received the ending where Keira and Lambert go off on their travels together. After the ending Geralt can ask Keira about her relationship with Lambert and she'll give Geralt a brief explanation about it, followed by Geralt's approval of their relationship.
![](https://s2.save4k.ru/pic/kox17tHtJDs/maxresdefault.jpg)