John,
Are you sure you didn't get up and into the shoulder blade? I guess it's possible a centered rib might stop the arrow but I wouldn't have thought so. I would have guessed major bone strike to stop the arrow like that...either big leg bone or scapula. Too bad, you've really a string of bad luck. I would chalk it up to another Murphy attack and get after it again. She will almost certainly recover.
By the way, how high up are you? The higher I go the more I struggle to keep my arrows down. I have done the same thing, though it was with a steel head. My shot got up into the spine as the shot was very close and I was high.
George