Hi Margaret! Are you still actively researching this line?
As you know, I am researching any Foster who resided in Benton, Henry, St. Clair or Morgan Counties in Missouri prior to 1850. Adrian William Foster qualified as he had several children (including Sarah) born in Benton County in the 1840's.
As we have gathered information so far it appears Sarah was not descended from the same line as Stephen Collins Foster which began in North America with Alexander Foster who immigrated from Londonderry, Ireland in the 1780's. Instead, her line is from a Richard Foster that immigrated to North America in 1635.
It would be great to compare notes again as it has been awhile since we touched base.