A couple quick points to ad to Mr. Dunbar's sage advice:

First, keep in mind that you can't copyright an idea. You can only copyright a "work." If you freely give someone your ideas over the internet, without some agreement between you about how the ideas are going to be used (and how you're going to get paid for it), you can pretty much kiss your idea goodbye.
Ideas, procedures, principles, discoveries, and devices are all specifically excluded from copyright protection. In fact, the copyright act specifically says "In no case does copyright protection for an original work of authorship extend to any idea... concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work."
[The sort of example that is often used to explain this distinction is as follows: Suppose you invent a process for harnessing brain waves or some other idea that could revolutionize society as we know it. We all know that if you write down on paper a description of your idea, that description would be protected against copyright infringement from the moment it is written (fixed in a tangible medium). If you then publish what you have written, no one would be able to make additional copies of the paper without your permission, because you have a copyright in your work. The work is the writing that you made. However, anyone reading your published work could use still use your brain wave harnessing process without fear of copyright infringement, because the copyright law does not protect the process (your idea) itself. In fact, someone could use your idea and write their own paper about it, as long as their work described the idea in their own words and did not take any "expression" from your original paper. This is why there is a separate field of protection for ideas and inventions under patent law].
In Linda's situation, it appears that there were some writings back and forth between the collaberators, which could be shown to a Court to demonstrate the intentions of the parties. However, we don't have all the details, and this forum is not designed to comment on specific situations. Nevertheless, this points out the danger of getting involved in collaborative works without having a specific agreement in advance.
Should someone like Linda (I say "Like Linda" because Linda is obviously too honest and caring of an individual to ever let this happen) decide to cut the collaborator out of the picture and exploit the collaborative work on his/her/their own, and should the collaborator then come forward with sufficient proof of an agreement (so that it can be shown that the collaborator didn't just feely give away his/her ideas), then the law will impose what is sometimes referred to as a "constructive trust"- meaning that the person who exploited the work is considered a trustee who owes a fiduciary duty to the collaborator - and must pay over a portion of the proceeds.
As you can imagine, this can get really messy. As you can also imagine, given the free flow of ideas that has been engendered by the use of the internet to facilitate pseudononimous authors working together across state and international boundaries, we are seeing an increase in these problems.
If you ever see something on the internet that says "send us your lyrics," or "send us your songs," you should not send them anything unless you first have the copyright registration. You should also be prepared for the possibility that your really good song idea could be co-opted. Worst of all, if you see something that says "send us your song ideas," avoid it like the plague.

As to the estates questions/answers/comments above, Estate Law is going to vary from state to state, and you really need an attorney to sort this out. It's going to have a lot to do with whether there was a Last Will and Testament, as well as rules of intestate succession - and the tax ramifications can be enormous.