Answer:
“She always took it upon herself to challenge anyone who disagreed with her” - in this sentence “anyone” is the indefinite pronoun.
Step-by-step explanation:
Without establishing what a thing or who it is, a word is used for referring people or things indirectly. These are Indefinite pronouns. These are formed with quantifiers and points out to a person, thing or place.
Here, “anyone” is used to refer to some person or someone whom one has challenged if there is any disagreement. Other examples of this kind of pronouns include everything, anywhere, nobody, something, everyone etc.