I thought the trial of the grasses is supposed to somewhat strip emotion and/or empathy(?)
That alone can change a personality, drastically.
Yeah.
Considering how much strong emotion Ciri shows in TW3, stripping her of a even just a third of it ought to change her personality to some extent.
It could also be the the Trial affects females differently than males. Additionally, Ciri doesn't undergo it as a child, which certainly should affect something.
We also don't know if the Trial is the exact same as the one witchers before her went through, since we don't yet know how or where hers took place.
Plus, age by itself can certainly affect personality, too, especially in early adulthood.
PS. I do hope she'll have changed (matured), as I had quite enough of her TW3 personality in that game...