Each relationship is different and you have to access wether your friend will respect your business and that she see's you as the professional you are. If you decide to do this you must be very clear about your policies and the implications of not following them. I would do an interview with her as you would do any other client and be all business. I would also let her know that there will be no preferencial treatment as if she had a business you would not expect it or any discounts because this is your livelihood. If your friend hesitates in answering or disagrees with your policies then I would see that as an indication of problems ahead. IMO I wouldn't do it but you know your friend and I don't. Good luck.