Well, if I was going to do it, as a first stab:
Roll +stock spent. On a 10+, they're fixed, fine and dandy. On a 7-9, choose one:
* The angel is exposed to the disease. (Don't choose for noncontagious stuff, or if the angel's fixing themselves.)
* The cure's got some unpleasant side effects. The MC will tell you what, something equivalent of -1 ongoing to certain types of rolls for a day or two.
* You've got a temporary remission of symptoms (for a day or two), but it'll take one more stock by then to fully fix the problem.