I agree that you need something to go on. I know several people who don't like chocolate cake, and even though I love it, and adore marzipan (many don't), I find Sachertorte sickly. And it's always so much better if the cake decoration is personalised to a person's interests and lifestyle - surely the friend who's asked you to make the cake can give some information?
If not, I'd go with Humbertbear's suggestion of two different layers, and then check online for decorating ideas. At the very least you could incorporate her name in there, or where she lives?