"She is much taller than I."
So, in speaking politely to a man, you would say "Lei è molto più alto di me." You are taller than I am. OK?
Right, but according to my grammar book there is an exception with the past participle: "Dottor Biagi, l'ho vista ieri in TV" (Dr. Biaggi, I saw you on TV yesterday), where the feminine "vista" is used. I haven't seen that one on Duolingo.