I think you may have found her grave!
She died in the birth of her son John Faupel, who died a month later. The dates match perfectly. The information that I have shows her born in 1850, which matches the grave stone. And the "J. Faupel" on the stone is probably the infant John. With three surviving kids, he quickly remarried on 5 Mar 1878 to Mina Miller at Iroquois County, IL.
Justus and Mary/Marie married in Washington, IL in 1870 and moved to Martinton in 1874. I think that she must be related to the Euchners of Martinton, but I do not know how, so that I cannot say whether there is a relationship.