I don't know that Esperanza is so much afraid of Sire (though he does have a bad boy reputation) as she is afraid of her feelings for him. He's her first real crush and feeling those feelings for the first time as a young girl can be overwhelming. Her parents think he's a punk, which probably adds to his allure to her. She's curious about what he does with Lois because she wonders what it would be like to be Lois, to have someone tie your shoes for you and to ride on someone's bike. But she's probably also curious as to what her parents mean when they say she's the type of girl who goes into back alleys.