Steve,

If your sister is interested in slide, there are some good teaching tapes available. Scott Ainslie has a tape of Robert Johnson's guitar techniques. It includes Kindhearted Woman Blues, Sweet Home Chicago, Drunken Hearted Man, Ramblin' on My Mind, Walkin's Blues, Come on in My Kitchen and Cross Road Blues.

Bob Brozman has an excellent tape as well on Bottleneck Blues Guitar. His focus is more on techniques and riffs than on whole songs, but he is very informative.

Roger in Baltimore