Rebuilding Kaer Morhen, expanding the witcher's influence, unifying the land, becoming an empress. None of these main quests coincide with each other.
Still, one would surely need their base, and that base had to be firm and unbreachable. For Olivia, that base would be the Kaer Morhen.
Olivia's goals involved global domination. Cirilla's was much simpler - be a mighty witcher, protect her sister.
Geralt and Vesemir highly admired Cirilla's thirst for power. They may not allow Cirilla to go through the Trials of Grass, not just yet. They compromised by putting her through the sort of training Witchers underwent.
They were shocked to see her completing whatever form of training they could throw at her without a hitch. Her talent for the sword was admirable.
