That is tough. Well, she knows she doesn't have the curtains, its no secret. I would be honest about it. But do what you think is best. The truth is you could discount your price or do them for free. If she isn't paying you then offer to do an extra project, like a matching pillow. You will feel a lot better when you finish. I have sewed for people before. I know the pressure. I have a project sitting in my car right now.