That would depend on your agreement with her. If the logo is of her design then the rights to that belongs to her and you get a fee paid to you for the work. You cannot sell that logo to anyone else. Generally for logo I would say the person or company who commissioned the work owns the copyright. If it is a image you made and she wants to use that as a logo, then you can sell her the complete copyright of the image or just the right to use it on a business card and no where else. And for that you also have to explain to her that you can use that logo / image for any purpose you deem fit as it belongs to you.