A sex symbol is someone is is extremely attractive, has sex appeal for example celebrities get judged on who is the sexiest person. The sexiest person (male or female) is the sex symbol, an example...
Although there is no official symbol for gay marriage, when Miley Cyrus wanted to get a tattoo representing gay marriage, she had a equal sign ("=") tattooed on her ring finger. A similar symbol...
Because she was not afraid to show sex. She wore sexy things, and said sexy things that, back then, were considered racy. She was so innocent, but she was a very sexual woman at the same time.