Copyright is your upon creation, filing it gives you a stronger legal position in court, and copyright doesn't prevent someone from stealing your design, or walking off to another printer with them. If that happens, it is up to you to enforce your legal right to stop them. IE: Spend money on first a cease and desist letter, followed by suing if that does now work.
You can file for the official copyright office. The link is on the left. You can file it right on the site. To save money, you can file more than one design at a time, it is the same price to file many as it is one. Okay, once you file the copyright, you have a stronger legal leg to stand on in court.
I am not a lawyer, I did not sleep in a Holiday Inn Express, I have read the good and bad stories of the copyright experiences of others on the forum, and copyright articles on the net.
This is my version of what I've gathered. Hopefully others will chime in to help round out the view, and give you more insight. If you search copyright on the forum, you'll find those threads, and if you read the copyright.gov website, you will find alot of valuable information as well.
In the future, whether or not you charge for the artwork, you may want to have the customer sign a artwork agreement stating they understand that unless your wife specifically transfers copyright ownership to them in writing, she remains the copyright holder. There are designers who charge for designs without signing over copyright along with the sale of design.
For the best advice on copyright questions, it really is best to consult a lawyer who handles copyright issues. I hope this helps give you some direction on this. Everything I've written can be found somewhere here on the forum, on the copywrite.gov site, or other educational sites on the net... Best wishes..
