I just wanted to mention such templates for documents are available online. I have used templates before, and this sounds like a contractor agreement because she is performing services for you, but media release forms can be found online as well. I used one from About.com for my current voice over job. You can add whatever language you wish to it, and then have a lawyer check it. If you dont have the money for such a thing, you should still get something in writing.
On a side note, voice actors who work online are mostly do-it-yourself people, so she may even know herself. I work with voice actors myself on some casting sites.