Regarding "Jeanie with the Light Brown Hair": I should add that "Jeanie" was Jane McDowell Foster, Foster's wife, often known as "Jennie"; in Foster's draft, he was dreaming of "Jennie," but someone, probably his publishers, made him change it.

As regards inspiration: Foster was a musical savant, and probably autistic (not all savants are autistic, but probably 50% are, and Foster's other traits when combined with the savant talents strongly imply an autism diagnosis), so he could absorb things based on unusual exposures. So it's possible that he heard "MacPherson" and did something with it. But there is no evidence for such a supposition.

Gershon Legman thought Foster was inspired by "To Daunton Me," but Legman heard connections that no one else heard.