Perhaps the reason that she doesn't reveal herself is due to someone peripherally involved in the group fell for Dorothea before she took on the disguise (and she's kind of creeped out by that person, perhaps a rival publisher), making her question things seriously whether she can afford to reveal herself.

As to the resolution, the idea of faking one's death makes me think of the Doctor Who finale and how it was awesome but could be seen coming a million miles away, but it could also fit into this story somehow (publishing rivalry leads to death plots, and a faked death kills two birds with one stone, though this now seems over the top as well). Basically I can see it as a double victory that comes as sudden inspiration (though perhaps not without internal conflict of giving up her Dorian life).

Regarding Pratchett, his writing gets a lot better as the books go on (well, at least up until recently, which is just tremendously sad), but it should be known that he has books within Discworld that form their own mini-series based around different groups of characters, and it's pretty important to read those in order, if not the whole series really.