Your Mary Caroline McNair was either a sister or daughter of Lorenzo Dow McNair. (I could tell you specifics, but don't have my files with me at the moment.) He was b. SC in 1808 and died Lebanon, Hinds Co., MS, in 1878 due to yellow fever--as did MANY others. The Hinds Co. McNair family has been researched thoroughly and you can find much of the info here in Ancestry.

I met two sisters at a McNair family reunion who were from Udall, Kansas (which is near McPherson, Kansas). I would not be surprised if that town name had some connection to your McPherson family. Good luck searching!