I don't think Ciri would undergo the trials of the grasses. I can't recall fully but didn't they steal the notes to the rituals in the 1st game or something like that? I think there was some mention about it the 3rd game about it, maybe a quest or something.
She's already killing monsters anyway and will probably have magic to balance the witcher quirks she is lacking.
According to book lore the knowledge of how to create mutagens that cause the transformation was lost during the mob attack on Kaer Morhen - people who knew about it died during the fall of the castle.
There are still old mutagens stored in Kaer Morhen and Vesemir uses them to create new generation of witchers (Geralt, Eskel, Lambert, Coën) but in the newly published novel (Crossroad of Crows) Sapkowski suggests that he really didn't know what he was doing and his contemporary, witcher Preston Holt wanted to stop the Trial of Grass altogether because it resulted in too many adolescent deaths. Which, among other reasons, caused Preston to be banished from the castle.
Sapkowski also suggests that mutagens deteriorate over time and the effect of their usage would get increasingly volatile. He mentions unsuccessful experiments, like the creation of Cats (a generation of witchers created in a different school that all turned out to be violent psychopaths).
So it would make no sense for Ciri to undergo the trials. She's too old and of a wrong gender. Most importantly, she's too important for Geralt to expose her to a process with a 10% survival rate.