What kind of dumbass country doesn't make sure its knights can at the very least annoy a magician? Based on how useless the prince's knights are, all it would take to destroy the royal family would be a really powerful magician.
@Acolytus
Probably the reason she wanted the prince so much is that most magicians aren't that strong, so they really don't need to worry too much about it because most would have trouble using magic in the kingdom anyway, she and the prince being probably extremely strong magicians (and i'm betting lynette has some special ability too), the witch had to bring in a ton of magic infused gems to come after him a second time, and she dissapeared some 10 years earlier so it's likely it's not easy to even aquire enough gems under a normal circumstance.