Having had a scab wouldn't sound like acne. I wonder if she had a little sore spot and scratched the scab off? Serenity had a litte sore similar to this on the back of her neck a few weeks ago. I put Neosporin on it three times a day for a couple of days and it healed up nicely. You would need to be particular putting ointment on this spot, though, with it being so close to Scratch's mouth. It sounds as if it may have become larger in the past few days? I'm sure you'll keep a careful watch on it and have it looked at if it seems to get any worse or shows any signs of infection.
Kisses to your little booboo, Scratch!