Mocha sounds like a one in a million good horse. It is amazing how some horses can tell when the rider needs a little bit more care.
Sad story of the stick. As a child I went to a summer camp where I rode a hot little welsh/arab cross. One day, under a different rider, she came ripsnorting to a stop from a canter, reared up and swung sideways off the trail, when she cam down her belly came down on top of an alder stump that someone had cut at just the height and with a sharp angle that she impaled herself on this stick. She reared back off of it, and of course her guts were pulled out of the hole, and she bled severly, to death, in minutes. Horrrible scene. I did not see this, thank God, but heard about it. Pixie was her name.
That sounds like a horror movie!! The other rider must have been horrified!