Who would win custody of a Native American child in Texas?

The parents weren't married, but they were together for about 3 years. The mother has nothing of her own. She hasn't been cleared to work, has no transportation, no license...anything. She is leaving the father for another man and is moving in with him (assuming). The father is a member of The Chickasaw & Choctaw tribes. Both federally recognized tribes. Ive read the ICWA (Indian Child Welfare Act).. But I didn't really see anything for child custody hearings. She has had this child taken away before when he was born due to tox screens... But of course they couldn't take him from the father because he is native american... In your opinion, who would get full custody? And if you could give me some resources to look at??