I think that after publishing that letter in the Daily Mail (or Mail on Sunday) she will have no choice but to at last send in her formal resignation.
To add to tory woes, Theresa May is on the verge of having a book of her memoirs published, due to come out just before the tory conference. There are, apparently, some jitters about that, too, because she has things to say about brexit and Johnson. And she won't tell the whips just what is in the book..
I should think that this might worry the tories more than Dorries' threatened book will, because May is unlikely to write a work of fiction...