not to add to anyone's stress . . . but . . .
i had one of my cornell supplemental eLORs flake out on me - so much so that two days before the deadline, when she hadn't submitted, and wouldn't return my calls 🙂scared🙂, I called my best friend who had volunteered at the shelter with me, and asked her to pretty please write a letter of rec on my behalf. she very graciously agreed, and couriered it to Cornell (plus extra copes to me for submission to Glasgow and RVC) so that it arrived on time. Cornell admissions had to go through a process to change the "registered" letter writer, and note my file that the letter was coming from an alternate source.
moral: if you're concerned about an evaluator, start contacting a backup. explain that you're really sorry to put them in a tight spot, but you're just up against a tree, and you could really use their help ("grovel, grovel / grovel, grovel / cringe, bow, stoop, fall / mercy, mercy / beg, kneel, sponge, crawl"). don't disparage your original evaluator (unless your backup happens to be your best friend - in my case, i vented for a solid half hour 🙂boom🙂 before actually getting around to my request, which by the time i asked, she was expecting) - but lay out the situation, and impress the urgency.
and do it now rather than wait until two days before.
just my 2p. 🙂