Mary's listing on the FindaGrave.com website does appear to show a small headstone with the name "Mary J." in raised lettering on the top edge, while the vital dates are engraved on the front face of the stone. The angle of the photo does not allow for a clear inspection of the dates, and the turf appears to be above the death dates, so I have some question as the accuracy of the dates on the website listing.
The listing indicates that she died in Bureau Cty, Illinois, but her younger sister Sarah was born in Ohio after Mary's death (if the date on the listing is accurate). This suggests to me that perhaps the family brought the stone with them from Ohio, or more likely the listing does not have the correct date of death. Another distinct possibility is that this stone is for a different Mary Weibel (or Weible), but the photo also appears to place the stone against the larger family monument. For now, this question is unresolved.