Here's why:
* Intensive pronouns emphasize the noun or pronoun they refer to. They are not necessary for the grammatical structure of the sentence, but they add emphasis.
* Reflexive pronouns refer back to the subject of the sentence and act as the object of the verb. They are necessary for the sentence to make sense.
In this sentence, "herself" emphasizes that Mandy, and no one else, went to look for the cat. The sentence would still make sense without "herself": "Mandy went to look for her missing cat." Therefore, "herself" is an intensive pronoun.