Yes, but I don't have access to the book, so why don't you post her sources? Obviously, her book itself is not a reliable account of the experiment, since she could not have witnessed the experiment or interview anyone who did. I'm aware she is not a FE'er, so there may very well be a reliable source which contradicts the article I found. I would appreciate if you provide the source, since you own the Garwood book.
I'm not sure it'll do you any good, as you won't have access to the sources either (she references a few in this section), but here is how it's listed in here bibliography (at least I think this is the source you need):
ULIV (University of Liverpool), SFF (Science Fiction Foundation Collection), FES (Flat Earth Society Papers), SS (Samuel Shenton), R.M. Lynch to SS, 13 October 1968; T.T. Gardner to SS, 13 October 1968.
That's what's referenced, but I don't see how it can help you. Buy the book.
Does anyone else think it's strange that one book written by one individual is taken in such high regard by this group?
When we're talking about FET history, then the only book published in recent times concerning that history is very useful, especially as it's an unbiased book written by someone who doesn't believe the Earth is flat. Honestly, there just isn't any other reputable publication which looks into FET history so exhaustively or impartially.