I think changeling are probably capable of healing nearly any injury or condition, if they try hard enough and expend enough dross, time, skill, energy
The main issue being that (as terrible as it sounds) most mortals just can't be deemed worth that kind of expenditure. It can't be justified when Changelings have their own battles.
Also, I'm sure there was at least one case of a tragic end for a "Miracle Healer" who got investigated by the badd'uns.