Presumably Isabel Perry had worked with Olive Campbell and felt that her own contribution to the material which Campbell showed to Sharp, and which persuaded him that he should visit the Appalachians, had been ignored.

That would probably be down to Campbell rather than Sharp; for all that some (see "Willie-O"'s post earlier) tend to blame Sharp for the fact that Campbell is not better known. Look at any edition of Appalachian songs collected by Sharp which include songs noted by Campbell, and you will see that she is credited on the title page (though not on the outside cover in editions published after Sharp's death).

The songs noted by her (and perhaps by Isabel Perry, it would seem) are specified in detail in the preface to the 1932, and subsequent, editions; in which 39 tunes out of a total of 968 were collected by Campbell, if we are to accept Maud Karpeles' attributions; which seems not an unreasonable thing to be doing. The 1917 book contained far less material, with (proportionately) more songs from Campbell.