Father of Mary Anne Fvenimore

Hi. My brick wall, is my great grandmother Mary Anne Fvenimore. No one seems to know who her father is...or is not telling. I asked my grandmother about her mother in law, she got mad and said you may not like what you find out. And that was that. Mary Anne Fvenimore was born 7 September 1869 in Cheltenham, Montgomery County, Pennsylvania, daughter of Anna Jane (Bowers) Day. She married William Frances Moore on 29 December 1888 in Germantown, Philadelphia, Pennsylvania. She died 1 October 1937 in Philadelphia, Pennsylvania. Her mother Anna Jane (Bowers) Day married Henry Clay Day (served in Civil War, PA Regt.) in 1864, after serving in Civil War. They had a son William Day in 1865. Soon after Henry joined the regular army. After serving he returned to find that Anna had given birth to Mary Anne, (whom wasn't his child). I can not find Anna Jane Day in the 1880 census, but Mary Anne Fvenimore is living with her maternal grandparents. Henry C. Day, not too long after was living with woman, with whom he had a child name Addie Day in Philadelphia. Many, many years later Anna and Henry got back together, and he buried her with his mother, and later was buried in the same grave. Any help would be much appreciated. One more thing Mary Anne Fvenimore, told my mother that she was part Native American.