"She thinks about something else."
Translation:Pensa a qualcos'altro.
pensare + su appears to have connotations of thinking on it, or to think it over. Since here she is thinking of something else, or about something else, 'a' or 'di' work better. http://www.oxforddictionaries.com/translate/italian-english/pensare
Ella is among the Italian pronouns that "typically appear only as regionalisms, in formal speech, or in literature."