No, go back and play WC3. Lich King said it himself that he planned out all the events that happen to Arthas, to lead him to be his Death Knight champion.
Go back and play the mission. Kel'Thuzad even allowed Arthas to kill him and even explained the whole plan of the plague to arthas, rather than keeping it secret.
This lead to arthas being tricked to going to Northrend, which the Lich King damaged himself to free the Frostmorne from its prison, to get to Arthas' hands, which later on corrupted him.
all a detailed plan from the start.
---------- Post added 2012-12-17 at 02:59 AM ----------
Well Jaina is an Archmage as well after all. So she would have this license as well to do so as well.