You can check out Jean Richie's website at Jean Richie homepage. Click on "Books" on the top bar, or go direct to
Folklife Books where it shows Jean's Dulcimer book at about the fourth item down. The description is brief, and doesn't really answer your question about tab:

"The Dulcimer Book - Jean Ritchie
"A clear instruction method on how to tune and play the dulcimer. Includes the words and music of 16 traditional songs such as Go Tell Aunt Rhodie, Old Joe Clark, and Pretty Polly, plus tuning instructions for six modes. Chapters on playing countermelody, fingerpicking, singing with the dulcimer, and much more. Fascinating historical notes, rare photographs, discography and bibliography are included.   "

For $12.95, it's probably worth it for the pictures.

Most beginner lap dulcimer books show a "string" with fret numbers for each note, or just show the fret number to press above or below each note in the written music. I believe this one is pretty much the same, at least for the "beginner" tunes, although I don't have it handy to look.

Jean does post here occasionally, and has been around within the last couple of days. If you click one of the "related threads" at the top of the page here, find a post by "kytrad" and click on the name, you'll get the list of all the threads she's posted to. She's probably been asked about the book many times here, and people do discuss it fairly often, so it shouldn't be hard to find an old thread with some talk about what's in it.

John