I agree about not making it stressful. If you get embarrassed, they will pick up on it and it could make it more difficult for them. I agree about sticking to the facts and keeping it simple. But be very clear in what you're saying, don't make it wishwashy or confusing (more than it already is!).

It might be a good idea to chat to the person she lives with to see if they have had "The Chat" at all - they may have done this. It might also be a good idea to chat to her school and see what (if anything) they have covered in school to date. From memory, they begin these sorts of discussion pretty early now... If they have begun having those sorts of chats at school, it will help you to gauge how much she knows and give you some ideas on how to broach it. It might also help you to work out how to raise the topic.

HTH and good luck!

MG