I think I can answer this one.

There are several witches. The witch who wants the book has nothing to do with unlocking the crypt - she is just there for her own stand-alone quest. To unlock the crypt you want the witch Kiya (yes - named after the queen or goddess of this forum) who will automatically appear (at least when you enter the town) once you reach the necessary rank by doing quests.

Reality is for those who cannot cope with fantasy. Fortunately, I can cope quite well.