Is it just me, or is the outline of her face super thick?
My guess is that the artist used a vector based line tool for the face which had a set amount of thickness to it, but somewhere along the process there was a scale down of the image near the completion and the artist did not adjust the line thickness accordingly; you are right. Compared to all other characters, Sunny D, I mean, Sunny Milk has quick the girthy literal-jawline.