Are any of her relatives in her parents' generation still living?
Aunts? Uncles? Cousins? Are they still in Texas?

It is difficult to narrow the field without more information.
What city or county in Texas?
Any idea of approximate birth dates? any death dates? Cemeteries?
Were they born in Texas?

I found an Otis G. Alexander with his family in the 1920 Census for Oklahoma. This may be a possibility -- but this is not Texas.
The Race of the wife and all children is 'Native American'. Father's race is 'white'.
Place: Burney, Love, Oklahoma
Father: Dave??? L. Alexander 44 b. TX, father b. SC, mother b. MO
Mother: Ella 37 b. OK, mother b. OK, father born in TX
Children (age):
Bennie M (12)
Otis G (11)
Bouie L (10)
Wildon V (9)
Hanel M (7)
Ida E (4)
May C (3)

Next household:
Earnest L. Alexander (19) [Native Amer.] b. OK, father b. TX, mother b. OK
Olla B., wife (16) [white] b. OK, parents born in GA

This family is in Burney in 1910 also:
Head: David L. Alexander 35
Wife: Ella Alexander 26
Children:
Earnest L. (10)
Enna M. (6)
Ben M (4)
Otis G. (2)
David L. (9 mos)

I didn't find them in 1930, but Earnest is still in Burney.
Head: Earnest L. Alexander (29) [Native American] born in OK, father b. "Mixed Blood" mother b. Chocktaw
Wife: Ola 26 [white] b. OK fbp. TN mbp. TX
Children: [all b. OK]
Cecil (10)
Glynn? (8)
Selma? (4]

There are also Alexanders in Lamar county, Texas. Lamar is in Northeast Texas, on the Texas-Oklahoma border. I believe it is just across the border (Red River) from Chocktaw, OK.

Tell us more, and perhaps we can help narrow the focus.