Being trampled by several horses that panic is not in the same category as a kicking horse. Being a long time rider she should have known better than to enter a trailer, a trap, in which there is another horse, even with one horse.
I just think that none of us were there to see exactly what happened so we can not say if putting the horse down was the right thing or if it was a hurt family makeing a decision on the pain they are feeling. I am sorry for the family and for the horse its a painful and sad thing to happen.
A friend of mine knew the owner's riding companions and from what they shared with her is that the horse was rather unpredictable to be around. They had all voiced their opinion that the owner should have done something about him a long time ago. He had hurt her several times before. The family thought it best that no one else needs to deal with his behavior in light of his history and the owner's death.