She showed a difficult face. Her main reason was because of her promise to the goddess, and she was afraid of what may happen if she did not uphold her end of the bargain.
But she can't tell him the whole truth.
"Be-because I already made a promise with Mr Tolius. I promise him I will help him in his mission, and he will teach me how to control my magic so that I can get better again."
"You mean the mission about purifying mages? You already know how dangerous that will be for you. We can just find another mage to teach you—"
"But Mr Tolius is the head of the mage council. He is already the best teacher there is, and he is the only one who knows what's happening to my body. Even if we could find someone to replace him, I don't know if I could last that long before we could find one. Plus, my body is like a ticking time bomb and an unstable one at that. I believe only Mr Tolius will know how to cure me."