A QH I had raised since the day he was born, developed Navicular when he was 8 years old; I wound up placing him in a therapy program. When they closed a couple years later, we had him placed with a family that wasn't extremely active. I was showing too much at that time, to have a horse who couldn't perform at his best...and he was one who loved to work, so I couldn't bear to see him stand around in the pasture all the time either. It was a very difficult decision, but I knew it was for the best.
Not sure if that is any encouragement, but I know you are trying to decide what's best for Chance in light of her health, so I figured I would give you my experience on that matter.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."