Yes, I agree totally with the word as used by DeWitt. The word in english and greek for "άφθαρτα" is "incorruptible" or "untouched" by the corruptible, and on the basis of Ethics I explained - as much as I could - the reasons why this word is the accurate one.
I may be mistaken but I think what Elli is saying is that "άφθαρτα" means "incorruptible" or "un-corruptible" in the sense of "untouchable" by anything "corrupt". Which, to me, makes perfect sense when you look at the last half of KD 1. That says "affected by neither anger nor gratitude." So what is being described is not a being that is eternal or imperishable in the sense that it lasts forever, but rather a being that is "untouched", that "remains the same" whether battered by gratitude or anger. That is very intriguing to me (if I'm understanding her correctly).
We seem to be getting hung up on what English word is used in translation. That's secondary from my perspective. Epicurus didn't speak English. We need to understand the connotations of the ancient Greek text itself and then decide the best English paraphrase, whether that's a single word or a phrase that best encapsulates the meaning of the original.