Hi Stephanie,
Sure can be frustating can't it? I saw the images of 1850 as you stated, in 1860 I was searching tonight (which is not indexed) images 101-294 the end, and couldnt find your Luvicia Simpson, I did see the Margaret Simpson from the prior 1850 census, with Lewis, John and Sarah the remaining children living with her. I don't think this is the Margaret Simpson that would be her mother. Often times a parent died, or was ill and a child was left under guardianship with a relative, uncle, aunt or grandparents. I would venture to say since William Sims is 51 and wife Sarah 50, in the 1850 census that she is residing in that household, and the oldest child being of 21 yrs of age, this could be her grandparents.
In the 1870 census, Anderson Simpson appears, looks to have a second wife, as the oldest child is 22, and the wife is 30. He probably remarried and your Luvicia came back to live with him, along with him having additonal children.
1870 Owen County Census Family 127-127
Simpson, Anderson, 40, Farmer, KY
Louisa, 30, Ky
Louis, 22
Lutitia? (think this whom is yours), 20, daughter
Granville, 17, son
John C., 14, son
Jasper, 12, son
Newton, 10, son
Abe or Alec, 5, son
Minnie, 3, daughter
Francis, 6/12 mos, son
I would speculate that the last 3 were born to Louisa.
My best bet is to find her marriage bond, and get the name of the bondsmen, often mostly is the father, or if he is deceased, or infirmed would be a brother. Depending upon which year she married, in the 1870's I know that have information on parents, and their birthplaces.
Good Luck