I read this letter by Sister Wyborn in a booklet by Brother Hoehn in the late 1980s if i remember right. While the style and tone of the letter is harsher than what i would personally write unless directed to do so by the Holy Spirit, what little i have checked of what she has written is true. She does goes into detail about what Vance Ferrell changed when he printed the 1884 Great Controversy, but i should probably check each accused change carefully before making a final judgment.
As you can read on this earlysda.com website, i have personal experiences with Vance Ferrell also. I used to buy boxes of his 1884gc. But when i found the 1858gc, i quit. His personal venom towards me for printing the 1858gc was quite surprising to me, and while i am totally guessing here, i wonder if it is not because he has invested so much in printing a different version. But even then, why would he change chapter titles etc.? I remember at the time thinking it was not a good thing to change the prophet's words even for the chapter titles, but now i think it is a very bad thing to do - showing somehow a pride of being able to choose words better than God can.