Is this 100km all in one day? I can tell you that 30 miles in one day is going to hurt your feet no matter what you are wearing. 62 miles is going to really really hurt. If it was me, I would bring a backpack with a couple different pairs of shoes--as in totally different from one another--to change them up. Give the feet a rest, something new to work against, relief from blisters if you get them, extra cushioning for when it starts to hurt, extra flexibility for when the cushioning feels like too much. Extra socks, too, so you can change them frequently to feel fresher on the feet. Whenever there's a rest stop, take off your shoes and socks and let your feet breathe. You might even pack a pair of sandals. Good luck.
Female, 5'3", 50, Starting weight: 163lbs. Current weight: 135 (more or less).
I can squat 187.5lbs, press 75lbs and deadlift 200lbs