Hi Thor, I think the daughter of Phyllis Lemieux and Fred Sanders was Gertrude Sanders, born about 1926. Given that name and date of birth, Ashland County should be able to send you a birth certificate if you request it.
Find a Grave Memorial: Fred Sanders 1901-1965 Catherine E. Sanders 1907-1979 Both buried Saint Agnes Cemetery, Ashland, Ashland County, Wisconsin, USA
1940 Ashland, Ashland, Wisconsin Fred Sanders 38 Catherine Sanders 31 Elaine Sanders 11 Frederick Sanders 10 Virginia Sanders 4
Based on your description, this Gertrude is likely the daughter of Phyllis Lemieux and Fred Sanders: 1940 Sanborn, Ashland, Wisconsin Kate Lemieux 59, head, born about 1881 in Wisconsin, widowed Micheal Lemieux 41, son, widowed, b 1899 in Wisconsin Bernard Lemieux 12, N son [sic] Gertrude Saunders 14, granddaughter, born about 1926 in Wisconsin Phyliss Bachard 20 lodger Residence in 1935 (a question on the 1940 census): Same House - Kate, Michael, Bernard, Gertrude, and Phyliss
Find a Grave memorial: Michael F Lemieux 1899-1981 Bad River Cemetery, Odanah, Ashland County, Wisconsin, USA
Find a Grave memorial Bernard F Lemieux, Sr. (1929- 22 January 2005) Spouse: Angeline Jewel Whitebird Lemieux 1928-2010) Bad River Cemetery, Odanah, Ashland, Wisconsin
There’s a Gertrude C. Edwards buried at Bad River Cemetery (1925-1978). I do not know if this is “your” Gertrude.
St. Mary’s Catholic Church in Odanah might have been their church and staff or a “congregational historian” there might know more about the family (especially since these people are part of such recent history in the community).