* "Piace" is a verb that requires a preposition. In Italian, the verb "piacere" (to like/to please) is used with the preposition "a" (to) when followed by the object of the liking.
* "La ragazza" is the subject. It's the person who doesn't like someone.
* "Lui/Lei" is the object of the liking. This is the person who is not liked by the girl.
Here's a breakdown of the corrected sentence:
* La ragazza: The girl
* non: not
* piace: likes
* a: to
* lui/lei: him/her
Therefore, the correct sentence would be: "La ragazza non piace a lui/lei" (The girl doesn't like him/her).