Identify the degree of comparison in the following sentence:
She is the fastest girl in her class.

We shall learn about the degree of comparison of adjectives in this question. There are three levels of comparison for adjectives: positive, comparative, and superlative.
The Positive Degree of an adjective, on the other hand, is the adjective in its most basic form. It is used to simply convey the existence of some quality of what we are discussing. When there is no comparison, it is utilized. The Comparative Degree indicates the presence of a higher level of quality than the Positive Degree. It is used to compare two objects (or two groupings of things). The Superlative Degree indicates the presence of the highest level of excellence. It is used when comparing more than two objects. The highest degree is mentioned in this question.
Positive cannot exist because a comparison is being made.

Comparative is used to compare two objects, but in this line, the subject is compared to the entire class (more than two things).

Because "she" is being compared to the entire class, superlative is the correct choice.