I accidently erased my sisters songs...

My sister gave her iPod to my Mom and I was in charge of getting her songs off and putting new songs on. When I pluged her iPod in I figured I would restore it. Well, it turns out that she had about 3 years worth of violin lessons on it that were not on iTunes. Is there any way at all to get it back? It's a iPod Nano 3rd Generation.