Nicole,
we've all "given it away" for the right reason at one time or another. As long as you came away from the experience with more knowledge than when you went in, you gained something. You also learned how these types of shoots work and who does or does not value the photographer as a professional. IMHO, that last issue is the most important. If you find yourself working with people that really don't value what you do, then you need to find different people to work with. Whether you're working with rescue organizations or doing your own portrait sitting in your own studio, you need to be sure that your work is valued and that you get out of it at least what you put into it.

Jim