Vicky,

Here's a "Mariah" long shot. The States are 'different' from your information, but the parents are not from Texas and Mariah is shown as being born in Missouri, rather than Texas.

From Ancestry.com:
United States Federal Census - 1870
about Mariah Tilman
Name: Mariah Tilman
Birth Year: abt 1855
Age in 1870: 15
Birthplace: Missouri
Home in 1870: Precinct 3, Harrison, Texas
Race: Black
Household Members: Name Age
A Tilman 24
Evaline Tilman 33
Henry Tilman 18
Mariah Tilman 15
Hariett Tilman 13
Oscar Tilman 11

We'll keep looking,
Art