Can't remember the title of a book?

Can anyone help me please with the title and/or author of a book about three girls who first meet at boarding school in Africa (can't quite remember which country, poss Rhodesia as was) and is about the story of their lives. I think one of the girls is from Ireland, one becomes a model and one has a fiance called Piet who is killed by a servant on the farm he lives on and the servant is called Simon. Any help much appreciated! Thanks