The other mage's dialog should of been a clue about her being so good with magic. She's had a long time to study and practice, on the criminals down in the dungeon. That, and if you do her little quest in Pinemoon Cave, when you return to her she spills the beans accidentally. Saying that they (the vampires in the cave) live in filth, but she prefers finery, and she also was the court mage when Torryg's dad was High King, which you can remark to her that she looks very young. Or if you have the CK, go to the race heading, then down to Breton Vampire, and there she is.
Here's another vamp you might of met, and didn't realize it. Hert at Half Moon Mill. She's a vampire. Her old man Hern is one too, but I've never met him, he stays inside.