'Her friend' is not wrong?! (DL accepted this for me) It can both be 'her friend' or 'his friend', because the person the question is asked to can either be a man or a woman. (Please feel welcome to correct me when I am wrong, Italian-speaking-people...)
You say 'la sua' amica (than you talk about a girl-friend) or 'il suo' amico (boy-friend) ....watch the 'a' or 'o' at the end of amico/amica...
Oh well, the polite form is written with a capital, as far as I have seen. 'La Sua'/ 'Il Suo' (native speakers can maybe help out in this part of your question?!)
In Italian 'Il suo/la sua' refers to the friend, and not (like in my language) to the person the question is asked to.