It just occured to me a scenario about how Kelson managed to survive. In canon, even though totally untrained, Jehanna was able to give Charissa serious pause before she was overcome. What if maternal desperation got her access to some even greater level of power? She might have been able to hold her off even longer, perhaps even being able to hit back a little. That would have probably riled Charissa's pride--that a totally untrained Deryni could actually HURT her--the point where she wouldn't just have put Jehanna into a trance, but have INCINERATED her. However, in the confusion, Morgan & Duncan would have been able to get the stunned Kelson out of there; by the time he got over the shock of seeing his mother killed before his eyes, he'd be halfway to Bremagne, who would take up for the cause of their martyred princess by giving him shelter.