People in the room heard her words and recoded it as witnesses.
Contemporaneous testimony by her SDA supporters.
Sorry.
Unless you produce a tape recording… pffft.
She also plagiarized other authors - frequently.
Since I have no intention of researching EGW, did she know Joe Smith and Brigham Young? They are all a bunch of cultists, and you know who is the father of the cults. 😀😃