I'm mostly guessing, but I believe that she is probably one of the Calloway County, KY, Alexanders, but she could have belonged to the Randolph Alexander family, one branch of which lived in the general area you mentioned. I have a rather extensive data base of Henry County, TN, Alexanders and don't find her listed. Since I would like to add her and her Lamb husband to my data base, I'll do some census and marriage checking, if you can help limit the period.
On another note, I noticed you posted concerning William Adams and Elizabeth Hall. Are you a descendant? They were my ggg-grandparents through their son Moses Henderson Adams.