I found somewhere on the Internet that you need to find out which type of a subject the subject in this sentence is. Your options are compound subject, simple subject, and complete subject.
A compound subject consists of two or more subjects (Jane and Jack). A complete subject consists of a subject and the words that modify it (That beautiful girl). A simple subject consists of one word only. Given that the subject in this sentence is the pronoun SHE, the correct answer is simple subject.