I think that it is better for you to tell her the truth than watch her waste her money by venturing into something that will not provide any profit. Don't fear looking unsupportive, she will be thankful later when realizes that you are right that the business is not profitable. You can even advice on a better alternative that is marketable.A friend came to me today to discuss about a business she is about to venture in, the issue is I have heard about that business and I know it is not profitable, but do I advice her not to go into it? Because she didn't ask my opinion and she was so excited when telling me about it. I don't want to look like a spoil sport.