There was a comment on this post asking whether Scarlett's acne has cleared up. The answer is that yes, it is very nearly gone. I ran out of the medicated pads from the vet a little while back and, per Rene's suggestion, have been swabbing the affected area with Hibiclens daily since then. I need to shampoo Scarlett's neck and chin to get rid of the remaining discoloration, but I think she'll be acne-free in about a week or so. I plan on continuing to use the Hibiclens at least a few times a week after that to make sure the acne stays gone.
You can see Scarlett's chin a little bit in this picture: