Thanks to Trove, I was able to track down another long-lost Dahl essay. This one was written by Roald Dahl himself and it’s called “My Wife, Patricia Neal.” It was published in the September 22, 1965 issue of The Australian Women’s Weekly. (I believe it’s the same essay that was published as “Patricia Neal’s Struggle to Live” from the September 1965 issue of Ladies Home Journal.)
I’ve added some scans from the magazine as well as an excerpt featuring Dahl’s description of Neal’s jumbled speech during her recovery, which he later used as inspiration for the BFG’s speech. (I found it pretty shocking that they gave cigarettes and alcohol to a pregnant woman recovering from a brain injury!)