1900 US Census Ward 4, Phoenixville, Chester County, Pennsylvania
McKernan, Caroline, Head, b. May 1835, age 65, widowed, 1 child born, 0 children living, b. Germany, parents b. Germany, emigrated 1875 McKernon, Charles, Grandson, b. May 1884, age 16, single, b. Pennsylvania, parents b. same, oiler steel works
If she didn't emigrate until 1875, she would be hard pressed to have a grandson, age 16 -- assuming that she and Bernard married in the US.