My prayers are with all of your family. It will be a long road, but I am sure she will recover and be riding again.
I had an experience when I was still in high school. I was a senior(back in the dark ages) and riding with friends on a trail in Big Sur, CA. We are talking skinny trails on the side of hills with long drop offs but had been on this trail many many times. I was riding along, with a friend in front of me on her horse when suddenly I felt the air around me. My horse had literally dropped out from under me and was sliding down the hillside while I was dropped into the dirt. After I got my bearings, I realized he had just misstepped off the trail and droped out of sight. We couldn't get down to where we last saw him and it was getting dark, so out we came. The next morning we went back with some help and started walking to the area where we fell but instead of following the trail, some of the guys went through the bottom of the canyon. Couldn't here anything, no sounds or whinnies, so we all had bad thoughts. About then, somebody yelled that they have found his bridle. Then someone else yelled and sure enough, they found him about a mile straight down from the trail, minus his bridle and two teeth. Scraped up and sore, but he walked out and was just fine.
It took me awhile to want to ride again, but I did, and I did not have any injuries like your sister. To this day, I still hate narrow trails.
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