Answer:
Association Fallacy
Explanation:
Sarah has "fallen prey" of an association fallacy. A very common error in our society. The association fallacy is a logical one, and it means, in simple words, that someone assumes that one person belongs to a certain group by simply looking at the other person´s appearance.
For example: Besides the very good example given in the question there are thousands or million of other situations in which we can see this happens: people often categorize other´s by their looks, hairstyles, piercings, skin color, clothes, accent, etc.
Sarah, i would think, was prey of the most common falacies of all: the association falacy.
