I am doing the Keira arc in W3. There are tons of references to the novels here. Also all the books found in the game are heavily inspired by the details in the novels.
I think novel/game fans would have had their minds blown when they met Ciri for the first time. However the character jump for Avallach is a bit too abrupt. They would have questioned that. But CDPR tries to ease it in with their writing.
Keira was a very minor character in the novels and her actions here mirror what was in that, except for a few points
1. they aged her up, as the game takes place around a decade later.
2. They made her more conniving, and like the author's view on what a sorceress is like. I think they aimed to make Keira a likeable but deeply flawed woman. One that can become a better person as she is helpful and can change her mind about things.
In the novels, she and Triss are the "weaker links" of the lodge with Triss being the weakest link. They are the youngest ones. Also the ones that don't completely fit in and get condescended to by higher status members of the Lodge.
3. her face design is rather interesting. It is a face of young british mommy approx. age 30. Like one of those girls that you can kind of see as a future stereotypical mom with 2-3 children. So this face, and the charming voice attached to it is rather disarming. Then, in contrast to her superficial appearance, she is actually very selfish and opportunistic, and conceals a great many things to her advantage.