The only thing that came up on Ancestry.com for ALTHA PETERS is a marrage record - she married RICHARD CONERLY on Mar 1, 1895 in Pike Co., Mississippi. I don't know if this is yours or not.
I decided to search for FRANK FOXWORTH - On the 1860 Marion Co., MS Census, there is a FRANK FOXWORTH, age 22, he is an "overseer" for his brother's "farm". His brother is listed as head of the household, JOHN P FOXWORTH, he is a "farmer"; his real estate is worth $100,000 and his personal property is worth $124,000. (Personal property included the value of slaves).
FRANK's full name is FRANKLIN WILLIAM FOXWORTH, born Feb. 15, 1839 in Marion Co., MS, died Nov. 16, 1905 in Marion Co., MS. He was the son of SAMUEL GREEN FOXWORTH and NANCY S POPE.
I tried to find a "FOXWORTH" child, born about 1863, on the 1870 Census - either "black" or "mulatto", but had no luck.
I even searched for ALTHA on any Census - just by using her first name, with no luck.
And SAM FOSTER is too common of a name to really narrow it down to one individual.
Perhaps you could provide more information on ALTHA PETERS or SAM FOSTER - or even the child that she had by FOXWORTH.
I'm sorry that this was all I was able to find, but we won't give up! Sincerely, Melinda