Ginny,
Here's the thing, if you enjoyed doing it and the potential is out there for you to do more, then I would give her the work and let her know, that you hope she appreciates the work you did and tell others, that you're available for this type of work in the future. Of course, any work in the future should be relative to the value of your design and $10 or $20 dollars is way too cheap. Besides, you may be competing with "real designers" who have a business and overhead and this pricing doesn't help that community of fellow artists. If you get an opportunity in the future to do more of this, then try and talk to other designers and keep your pricing realtive to your ability and everyone will be happy,
Rich