Spoilers for Charmed Life
Gwendolen is not actually a very powerful witch at all. Most of her life, she's been stealing power from Cat, who is a nine-lifed enchanter like Chrestomanci. By the time he finds this out, she has already used up several of his lives.
- Cat lost a life when he was born. Janet's brother died the same way.
- Cat lost one life in the boat wreck that killed their parents.
- Gwendolen used one of Cat's lives to power the spell she used to tie his remaining lives to a book of matches so she could control them more easily; as a side-effect, it gave Cat a terrible case of cramps.
- Fiddle was created with one of Cat's lives.
- Gwendolen uses one of Cat's lives to get to the next world over.
- When Janet deduces the truth about the book of matches, Cat attempts to prove her wrong by lighting one of the matches, which causes him to lose another life.
Chrestomanci has a pet dragon which was orphaned by poachers. It lives in his workshop, in the old part of Chrestomanci Castle.
Chrestomanci's weakness is silver: he can't perform magic on silver objects, and if he is touching or carrying silver he can't perform magic at all, and is obliged to speak only the truth. This limits his ability to deal with the tricks Gwendolen pulls at dinner, when he is surrounded by silverware.
Janet, when she finds out, suggests that he should switch to using stainless steel tableware.