I started bawling the instant you said she fell because when a horse falls nothing good comes from it. I am so sorry for your friend and please do tell her that I send my best wishes and support. This story triggers a sad memory that scarred my first stable for the rest of thier lives. They used to have a very nice barn on the land that is now a giant pasture but it caught fire and they lost 2 horses and a foal. They weren't my horses and it happened before I had arrived (not by much) but I still feel the pain. Every newcomer cried when they heard about how they lost 3 innocent lives to the flames. It's a horrible thing to lose your best friend but sometimes it is best for them to be put down so that there's no more pain. The best you can do is be there for your friend and the other horses because you all had to witness it and you won't be able to heal without each other.